As much as I'd love to talk about the passage of time, what it means and how it affects our main protagonist Frieren compared to everyone else in the series, there's not much I can say that hasn't already been said better - countless times by other people.
This also isn't going to be a review about the elements that made the Frieren manga great (that includes story, narrative, characters, writing, setting, etc). I'd rather spend that time talking about what Madhouse did to elevate their adaptation of the manga go far and beyond what the original manga was able to achieve.

When you think of Madhouse you usually think of faithful adaptations of classics that stuck true to their source material. Rarely does Madhouse put out an adaptation that is unfaithful or worse than the manga that it is adapting, in fact most of the time their adaptations are on par with the source material. It is that last part that I'm gonna be focusing on, "on par with". Madhouse has always put out great adaptations that faithfully adapt the source material but almost never risk it and try to go above and beyond and create something better than the original.
As an example I will take their adaptation of Naoki Urasawa's legendary manga series "Monster". Madhouse's adaptation of Monster is critically acclaimed and adored by fans for it's "near perfect" panel for panel adaptation of the manga. In fact it is such a good adaptation that the manga and anime are even interchangeable (which is pretty rare). If you prefer movement and voice acting - you watch the anime, if you prefer reading and page flipping suspense - you read the manga. You don't miss anything either way. But beyond the media differences (the addition of voice acting, animation, music, among other things), there's nothing in the anime adaptation that makes it stand out and make it the definitive way to experience Monster.

Now, enter Frieren.
Frieren is a major stepping stone for Madhouse and the anime industry as a whole. It will hopefully set a new standard as to how anime production should be. This is the first show Madhouse has made (maybe Chihayafuru?) that has truly elevated the source material above and beyond to the point where it's THE best way to experience the story - no ifs, ands or buts. Madhouse pulled out all the stops for this one, hiring Keiichirô Saitô - the fastest rising new director to direct the show, Evan Call - the composer of the legendary Violet Evergarden OST, and assembling the Avengers of animation. This combined with a healthy production cycle is great but it's not like there aren't any other shows with a healthy production cycle that have great staff.
What makes the adaptation of Frieren so great is that while it DOES perfectly adapt every little detail of the manga into animation, the pacing never seeming too fast or too slow, what really sets it apart is how it turns the manga's weaknesses into one of the shows biggest strengths.
For reference, the arc of the manga that is considered the worst of the series is an action heavy arc with lots of fight scenes. The fights are often confusing in the manga and often mess with the series' tone and tempo. Madhouse transforms this arc into one of it's strengths and turns it into one of the best arcs in the show with mind blowing animation (possibly the best animation of the year might I add) and fight scenes with powerful moments all fitting together like a puzzle, nothing seeming out of place, unlike the manga.
I wish I could talk more about it but I'd be entering spoiler territory - which I don't want to.

The Frieren anime is the closest we've gotten to a perfect adaptation of a series, a show that doesn't just adapt every panel into animation, but transforms the manga's weaknesses into the show's strengths.
It is in my humble opinion tied for the best anime of 2023 (along with Vinland Saga S2) and so far the best anime of 2024.
The anime is THE best way to experience the story and I can't stress this enough. The only reason you should be reading the manga instead is if you don't have the patience to wait for a second season (which is all but confirmed).

Do yourself a favor and watch Frieren: Beyond Journey's End