I've been playing since the NES and despite being from a low income family I had the luck of being able to play and own many consoles over the 3 decades of my life, plus some pc.
If you ask me right now? Resident Evil 4 (2005).
A before and after in gaming, to this day still extremely fun to play even for casuals but 20 years ago it was THE masterpiece. And everyone took notice of it, everyone played it, even players that didn't cared about resident evil. The gameplay was so good that it got photocopied by everyone right after in the action genre.
Arguably the last big innovator in videogames minus Minecraft and... PUBG (Fortnite did it better I know).
Try to NOT pick your favourite game, that's a different thing.
I'm a sucker for Morrowind and I'll always be. Because I'm old and boring, but also because I just love the weird quirks of an epic game that doesn't take itself too serious. Skyrim is a calf.
Strong disagree with Gungeon. It's hard skill capped, pickups mostly offer very limited benefits, and there's very little in the way of permanent upgrades. Normally, in a roguelike, subsequent runs get easier because of your unlocks, and getting a good drop really helps. I didn't really feel that in Gungeon. No matter what, it's still extremely difficult. There's very little progression other than "git gud", and at this point it's just a shooter.
I bashed my head on the first biome until I managed to unlock starting from the second biome, until I realized doing that would just leave you too weak to deal with the second biome, as if you didn't find anything useful at all in the first section.
It might be a good top-down shooter, but as someone who loves roguelikes but isn't the biggest fan of shooters, I really wouldn't say it's doing a great job as a roguelike.
Yeah it's very skill based but unlocking guns really helps out by helping with the RNG and unlocking characters also like the health tent. Finding the bonus levels is also really good since it'll get you more supplies while making the run longer.
For sure it's not for everyone but this thread is a lot about opinions anyway so I'm leaving this one as mine since I love the feeling of overcoming seemingly impossible challenges with skill like Dark Souls, Hollow Knight and Celeste.
I did experience the same feelings as you did and I so many times I thought "This is bullshit" but I put faith in my brain to figure it out and there was a small but noticeable difference in every 1h session. More health, more chance of beating bosses without getting hit and such. In the end I beat the high dragun which made everything worth it and somehow it's still fun and challenging to play. That's why I put it as my pick as the GOAT.