I don't follow the question. (Not this thread specifically, the question just seems to come up a lot.) Just about anything will look better if you throw more pixels at it, and just about nothing actually needs those pixels for anything. There mostly aren't big technical limitations related to 4K at this point unless you like to run with all settings maxed out. Resolutions are freely adjustable, square-of-pixel-count render costs are rare, and textures sized with 4K use in mind are the norm. What makes one game a better fit for it than another, then?
My own vote would be either games that have a lot of visual complexity related to the mechanics and need all the help they can get presenting it to the player (these are rare for obvious reasons) or games in which being able to resolve fine or faraway detail is an advantage (PvP games with very large worlds, probably - Planetside, Rust?). Games trying to represent particularly fine detail for aesthetic reasons would fit the bill, but fine detail usually doesn't make the aesthetics. Based on what gets recommended, I'm clearly not coming at this from the same angle as everyone else, though.
As for stuff recommended here that I've got any experience with:
GTA V: This one makes sense, assuming settings are cranked up far enough that it's rendering detail at great distances. What I've seen of it wasn't even close to doing that, but that was on a console, so the PC version on sufficiently high settings might yet do the trick.
Forza: Racing games are an odd edge case where the "fine detail for aesthetic reasons" thing really matters, IMO.
Rocket League: I don't follow. Completely lost on this one.
DOOM: Just as lost here. I tried it at way too many mixes of resolutions and settings on a 1440p monitor, and there was surprisingly little fine detail to be seen at 1440p. I'm usually picky about sticking to native res and can't stand TAAs for their blur, but I didn't feel like I was missing anything playing DOOM at 720p with TSSAA and a bit more film grain / sharpening than necessary (still pretty low on their scale). Basically, settings designed to completely obliterate and then fake back in fine detail weren't a problem because there wasn't much of anything (useful?) there to obliterate in the first place. (I also played it with motion blur on high in an unsuccessful attempt to cover up an animation hitch that drove me nuts, FWIW.)