MGS2 - I went into this game with no prior knowledge and it was unlike anything I'd ever played. Nothing made sense and I loved it. The ending AI speech is insane and incredibly ahead of its time. I could play any game in the series multiple times, but MGS2 has stuck with me the most

Celeste - The whole package of this game is just amazing. The music and level design is top notch, and completing a hard level is so satisfying.

Shovel Knight - Similar feeling to Celeste, but I really loved how the DLCs completely changed the gameplay to make each playthrough fresh.

Mario Odyssey - This game was just an absolute joy to play throughout! So inventive and perhaps the most fluid and varied movement options of any platformer I've seen.

BOTW - It came out at a time when open worlds were pretty common, but it still felt so different. No other open world game has given me the sense of freedom and exploration that this game did (maybe Skyrim would be a close second - playing that for the first time was magical). I'm currently playing TOTK so maybe that'll usurp this, though I love both.