Dress Up Darling is a fun show that started strong but ultimately fizzled out. Just running down what I see to be the pros and cons of this show.
Pros:
- The opening and ending song are both great. Both are fun songs that you could listen to standalone, apart from watching the show.
- Marin Kitagawa is very cute. She is truly a fun-loving girl and always has a smile on her face. While she has a liking for provocative things, she also respects Gojou's wishes. For example, in one situation, she wanted to do something very provocative, but Gojou said he didn't want to see her like that, so she didn't. She also seems to have a childlike innocence. (However, I do have a nagging suspicion that she is actually a very lonely person as her parents are not around and uses her "childish fantasies" as an escape to fill that loneliness void, but that's just my opinion. Doesn't diminish her as a character, if anything, makes her more sympathetic).
- The unique subject matter is cool. There aren't a lot of shows that focus on cosplaying, so at least the show isn't your run of the mill guy loves girl and maybe some other girl from before and have adventures in school like so many other anime - Nisekoi, To Love Ru, etc.
- Not much in terms of relationship drama or love triangle. The focus is on Marin and Gojou's relationship.
- The artwork is quite nice. Marin has such a sweet smile. The backgrounds are usually bright and cheerful.

Marin-chan

More Marin-Chan
Cons:
- Gojou-kun is a kind but rather lame character. The whole story starts with him having childhood trauma of a friend mocking him for liking hina dolls. The first episode has Marin-chan accept him for liking hina dolls. Then, that's it. He isn't really shown as making any progress in hina dollmaking, nor does Marin ever really take an interest in hina dolls. He doesn't really come to terms with his trauma either and the childhood friend is never encountered in the present day. He is just depicted at Marin's dressmaker and sort-of boyfriend, and he therefore doesn't really grow as a character on his own. (Neither does Marin, but at least she has a lot of fun doing what she likes. We don't even really see Gojou doing what he likes, which is making hina dolls).
- Towards the middle of the story, two new characters are introduced, but both characters are rather cliche. One is a generic tsundere, while the other is a generic shy girl. Neither seem to have caused any noticeable change in the main characters, and in fact, in the episode where those new characters appear, they seem to take away screen time from the main characters. Also, the new characters disappear as quickly as they appear albeit after several episodes and were never mentioned again.
- The story gets repetitive after a while. A new in-universe character catches Marin's eye, and she wants to cosplay as that character and asks Gojou to make her a costume. Gojou just says yes and makes the costume. Marin wears the costume for like an episode or two and takes some pictures or has some fun. Then, the costume is put away and never mentioned again. This happens several times over the course of the show.
- Gojou also just appears to be catering to Marin's wishes, which is totally fine as it's his life, but he doesn't really himself take an interest in cosplaying. I would have liked to see him also try it, maybe being a bit reluctant at first, but doing a couples cosplay with Marin but that never happens. (In that regard, it looks like Gojou is also a very lonely person who does what he does because he likes Marin's company.. Reminds me of the song Strangers in the Night actually - strangers in the night, two lonely people... but I digress)

Basically the start of every arc...
One more note: Many reviews focus on the ecchi, but I don't see that as being a big issue for this show. The reason is that while there's some risque content, they don't ultimately show any private parts, and any risque content usually resolves rather tamely. For example, in the second to last episode, the main characters find themselves in a sexy situation but they ultimately just get flustered about it. Also, of Marin's outfits, only one is really risque and plays a fairly minor role in the show, one is sort of risque but is only featured in one episode, one has risque themes but is fully clothed, and one is a full uniform outfit.
I could however, see this tendency for Dress Up Darling to "tease" to be a con, as prudes find it annoying, pervs have more "exciting" things to watch like DxD or Monster Musume, and normies might be confused by the whole thing if not previously exposed to ecchi. The end result is that the ecchiness isn't at a level that appears to cater to anyone in particular.
All in all, a fun show especially for a change of pace and some quick laughs. Just don't expect a masterpiece or anything particularly extraordinary.