Digimon Adventure 2002 or 02 is a sequel to Digimon Adventure 1999 and continues with a new generation of chosen children to protect the digital world from sudden disaster. The digital world is inhabited by digital monsters called Digimon. Unlike Pokemon, they have more than 3 stages: Infant (In Training), Baby (In Training II), Child (Rookie), Adult (Champion), Perfect (Ultimate) and Ultimate (Mega) with the first being the names of the Japanese dub and the latter in English.
This series introduces a new ways of evolution and one additional new stage that in this series can be considered somewhere between Child and Perfect called Armor. Basically it can't fit to the traditional Level system like the previous forms which can lead sometimes to weird things when it comes to power scaling Digimon.

Like the previous season, the children get Digimon partners that help them develop and do the fighting. Each having a unique personality. In the living world they stay in their In-Training II level and in the Digital World they are in their Rookie state.

Unlike in the previous show, the children can go in and out the digital world with their upgraded Digivices whenever they desire.
Another upgrade over its predecessor is the addition of more variety of soundtracks for evolution. The previous types of evolution have the old soundtrack but Armor Evolution, Jogress aka DNA Evolution and Ultimate Evolution have their own unique soundtrack.

Digimon Adventure 99 was known for its great use of its protagonists. Sadly 02 can’t live up to the quality writing of its main cast.

Daisuke aka. Davis is basically a goofy version of Taichi aka. Tai. He starts off as a naive kid who is brave but over the course of the series he also worries about others taking their feelings in consideration as he was the first to be willing to trust someone who turned a new leaf. In short he has both Taichi’s and Yamato’s aka. Matt’s crests from the previous season and gives his take on friendship and courage. His weakness, however, is that he can be clumsy and has a crush on Hikari aka. Kari.
V-Mon encourages Daisuke often and shows a lot of personality. They are similar but often he feels embarrassed being part of Daisuke’s stupid plans to impress Kari. However, he has complete trust in Daisuke in fights even if it happens to be misplayed from the viewers perspective. He is one of the strongest members as he has the most evolutions.

Miyako aka. Yolie an energetic nerd. However, despite being experienced with computers and helping out a lot with Koushiro aka. Izzy who has the crest of knowledge, she is associated with love and purity aka sincerity. Crest that don’t seem to fit her selfish, greedy and cheeky personality.
Hawkmon is polite and has a cool design. There aren’t much notable interactions between these two.

Iori aka. Cody is the deepest character of the original new members. Despite being the youngest, he is skilled in kendo and can defend himself when the situation calls for it. His father who used to be a police officer died in an accident during the line of duty before the start of the story which shaped his black and white view on the world. Over the course of the series, his world would start showing more tones of grey which leads him to help reform an antagonist to the side of good.
Armadimon is a goofy armadillo who has some of the wildest evolution. Sadly he doesn’t contribute much to Iori’s character besides getting new evolutions out of them.

From the previous season, two other characters get upgraded Digivices and work as guides for the new members. Them being Hikari and Takeru who grew up.

Takeru aka. TK is more self confident unlike in the previous season and his knowledge sometimes end up helpful. Also some experiences from the previous season show a side not seen by TK so far and despite his on the surface cool self, there is a side of him that can’t forgive anyone who abuses the power of evil.
Patamon didn’t change much from the previous season. Sadly he can’t use his old forms for most of the season due to various cases the show used to power down the old cast. However, he did get an Armor evolution and later get a Jogress evolution.

Hikari aka. Kari was the last introduced member in the previous season and pretty much a deus ex machina. In this season she has an actual personality being a curious child and showing the most amount of emotions ironically. However, she is often the victim of being dragged into weird dark worlds with creepy images leading to situations the other members have to safe her. Luckily that doesn’t happen often.
Her partner Tailmon aka. Gatomon got powered down losing her holy ring putting her power down to child level despite being an adult level Digimon. But she does get new evolutions that help her out in fights. In the previous season she used to be an antagonist and the deepest Digimon partner. In this season not much of her personality shines except when she meets the ghost of her best friend and someone she hoped to never see again.

While 02 lacks good protagonists, it makes up for great antagonists. Some of which set the standards for many future Digimon antagonists to date.

Ken the Digimon Kaiser (or Digimon Emperor) is an evil chosen child who uses the Dark Spirals and Rings to enslave all the Digimon like Devimon did in Digimon Adventure 99. But unlike Devimon, Ken is far more effective. He builds towers, Dark Towers, that unable Digimon to evolve to the next level unless they use Armor Evolution making all the former cast members Digimon useless. He upgrades his gadgets when he sees there is an issue in them and even goes as far as building his own Digimon partner Chimeramon aka. Kimeramon. Ken has a tragic past where he used to be overshadowed by his overly skilled brother. Once that brother died, he filled that role in the family becoming a new prodigy to the point anyone else looked inferior to him including his own parents. Seeing him rise, develop and fall is one of the most interesting story arcs not being successfully replicated by other Digimon series yet.
His real partner Wormmon is supporting him despite knowing what he is doing is wrong. He hoped some day that the kind Ken he befriended with would one day return. There is a great character arc between these two when Wormmon has to make a harsh decision in order to protect Ken.
While he lacks Armor Evolution, he still ends up getting one of the strongest evolution in the show.

Arukenimon and Mummymon are a duo of villains similar to Team Rocket. They are henchmen to a bigger villain but until that gets revealed, they work effectively creating powerful Digimon using the Black Towers that were meant to seal the power of evolution. They end up creating one of the deepest Digimon characters in the show.

BlackWarGreymon is visually just a black pallet swap of the original WarGreymon. Created by Black Towers, he is considered an evil Digimon. However, being mightier than his creators he disappears in the hopes to find the real reason he exists. This leads to him fighting the protagonists very often and his overwhelming power leads him often the win. It is very interesting to see what his search for meaning leads too.

Oikawa is an adult man who desires to go to the Digital World and is willing to do that by any means possible. He has a traumatic past losing the only person who shared his love with the Digital Creatures who was Iori’s dad. He is really clever using various means to distract the protagonists from the main goal and even making them fight his enemies, the Deamon Corps who came to the world of the living creating chaos. Despite being a mere human, he uses his knowledge and assets well to get what he wants.

However, there is a reason why 02 isn't as good as it could be. Rather pretty mediocre.
After the Armor Eggs ended their purpose, we still didn't see the old kids using their Digimon to beyond Adult, but instead the new kids got Adult forms themselves and the show introduced a new evolution mechanic. So the show introduces cope outs to prevent the old cast coming with the latest evolutions and overshadow the new cast. But they will get some back for some nostalgia trip.
And more and more restrictions were put in and adults have all forgotten about Digimon.
And like with Tamers, 02 tried to tie in the Wonderswan games to excuse why Ken got evil. Ken's backstory got more and more confusing with many plotlines being dropped. The Dark Ocean plot went nowhere because Toei found it too depressing but aired "out of respect" the episode that confused everybody. Deamon Corps were, while powerful, filler villains that only filled the runtime like how MetalEtemon only existed as a sacrificial villain for Jou to make the non-Ultimate owning kids relevant somehow.
And the old kids rarely did anything of value and the parents besides exceptions like Iori's were pretty much irrelevant.
Female characters are meh unless we include Arukenimon. Miyako is selfish and hyperactive like a female Daisuke. She is more useful than Sora and Mimi but her role can be replaced by Koshiro in several situation. Hikari is less active than in Adventure despite being here since the beginning this time.

As a show where monsters fight each other, Digimon fights at the start aren’t that impressive. However, just seeing the different forms and the emotional struggles needed to archive the forms are usually worth it where the lack of good choreography can be looked past. There is a reason why many evolution, especially when they first appear, will stay with you. As the show progresses, the fights and budget improve. There will be a lot of recycled animation and the evolution to Child and Adult states seem rather lame. Like mentioned earlier, the new forms get a kick ass soundtrack unique to them.
Armor evolution is upgrading the Digimon for fast travel or other purposes.
Jogress or DNA Evolution is an evolution method where two Digimon merge into one more powerful one. However, each Digimon gets a set partner they can perform it with and nobody can chose who their partner will be. However, fusing Digimon is still cool.
There is the use of CGI for certain evolution which normally would be a turn off, but since Digimon are digital creatures, the evolution scenes are tolerable and give the show a unique identity as many later Digimon series will use that concept for their transformation scenes.

While Digimon is a kids show, it can be off putting or flat out scare the viewer as it goes on since the enemies can be deviant and scary.
Digimon can reincarnate but only in the Digital World. Digimon drying in the living world cannot. And one human will outright die in his show.

Digimon 02 is decent. It struggles to live up to the standards set by 99 and doesn’t take advantage of its old cast well to guide the new cast. However, it has amazing antagonist with lots of grey in them and are used as examples for future Digimon Villains yet to come out.