Since
Morrowind and various games with horror elements have been mentioned, here's some other games where the visual styles is an essential part of the package.
S Tier:
Idea no Hi
Freely embracing its artist's comedic background (one of his works,
Even a Monkey Can Draw Manga, even got a western translation and some professional recognition as a brilliant satirical work and continues to have sections passed around on image boards to this day) it both embraces and lampoons jRPG conventions while avoiding "normal" enemies almost entirely. Had it not been for the sheer
style of this game it would have been relegated to the dustbin of forgettable SFC jRPGs as its gameplay is merely OK in an era of greats. It's Earthbound before Earthbound, but even more crude and crass in its humor.
Baten Kaitos: Eternal Wings and the Lost Ocean (and
Origins)
Taking place on a series of floating islands, each with their own aesthetic, a game that uses its prerendered backgrounds to freely showcase the art while the weird world mechanics spice up an otherwise fairly straightforward story. Unfortunately LOLcalizers ruin the recent HD Re-Release.
The World Ends With You
Putting Nomura's belt fetish art in the one setting it has any business being in: Modern Shibuya youth culture with an actual no friends protagonist. The fun gameplay is, unfortunately, essentially un-portable due to having been designed to use every weird feature of the original Nintendo DS as actual features instead of just gimmicks. Sequel was ruined by DEI/"ethics department" and being a sequel to a personal passion project about youth where the people in charge clearly had neither passion nor youth.
Freedom Force (and sequel)
Attempts to imitate and capture the look and feel of a post-war American comic book. It generally succeeds at it, and it does this without depending on gaudy filters or fixed cameras trickery. UI is both super readaable and unique, which is a rare combo.
A Tier:
Digimon Story: Cyber Sleuth
While Suzuhito Yasuda's big titted and same face girls in overly designed clothes is absolutely the weak point of the Devil Survivor duology and clashes horribly with the demon sprites (largely reused from older games with much darker styling), I think it actually works really well here. In general his style translates well to 3D, and the (generally oblivious to what's going on) "real world" humans (most of whom are late teens, several of whom are explicitly into fashion) from non-ruined near future Tokyo are a place where it absolutely fits. These characters pair well with the cyberworld asthetic and bright and colorful toy commerical monsters, all of whom work to contrast the darker monsters that are alien even to the "normal" monsters. Really this only gets this high because the whole game is "low budget but charming" (It was originally an outsourced handheld title that got ports because Vita was essentially dead in the west by the time a translation was ready) and would not be nearly as high if it had a bigger budget.
Akiba's Trip 2
A bunch of developers from Akihabara made a game freely embracing the whacky and excessive parts of early 2010s Akihabara and Otaku culture. It's recommended you adjust the lighting options (An in-game set of sliders. The PS4 version the PC version is based on a lot of weird random features like that because it was done to get a hang of the PS4 and its new features) to be closer to the bright and colorful PS3 original instead of the harsh and drab default. Again, molested by LOLcalization in a recent re-release.
Valkyria Chronicles
Canvas attempts to make the game look like a water color in motion, and it generally succeeds. Unfortunately, it barely does anything interesting with the visual style and it's mostly just a filter gimmick. The very anime and often very modern (instead of quasi 1940s) character designs (who are mostly head swaps with slight height variance) don't really pair with it either, and Canvas is at its prettiest when you look at mechanical objects, structures, flora and faceless goons instead of any of the player characters.
