I was going to say replaying but I feel like that limits the question to games like Prey or Fallout New Vegas that have endings and games like The Sims 2 or Cities Skylines where you can play indefinitely end up excluded.
I’m not really referring to games like League of Legends where you’re coming back every month. More so games where you stop playing for an extended period of time.
Mirror’s Edge, Jet set radio future (and now bomb rush cyberfunk)
The 3D Mario’s (I haven’t gotten around to playing galaxy 2 yet and it’s eating me up inside lol)
Skyrim, Minecraft, stardew Valley
Ocarina of time and majoras mask.
Animal crossing (usually whatever latest entry, but I liked new leaf the best so far)
Lumines has become an addiction
Forza Horizon (similar to animal crossing, usually the latest entry, but surprisingly I enjoyed 1 and 4 the most. I was surprised about 4 because I didn’t think I really cared too much about the location, but I liked the seasons a lot. It kept everything feeling new)
Kirby and the crystal shards
You’re the first person I’ve seen say Mario, which I find surprising.
For me, it’s Super Mario World, including romhacks. It’s platforming perfection. I particularly like the SMW Central level competition compilation romhacks since you can skip the levels you don’t enjoy.
Spyro is another one I come back to, especially now with the remastered version.
Diablo 2, with mods now, is another. “Stay awhile, and listen.” I sure will, old man.
For a long time, it was Counter Strike and Team Fortress, but I don’t really play FPS games any more so it’s been almost a decade for me at this point.
Super Mario world is a classic! I haven’t tried any romhacks for it, that sounds like fun!
Oh man Diablo 2. I’ve attempted to play it so many times, but I’ve yet to finish it yet. Not because I don’t want to, but it’s like every time I start up a fresh game, something happens to my game or save. I’ve lost a save twice now(this is over the course of 15 years) and the last time I tried to get it to run, it didn’t want to cooperate on my windows 10 install. It’s oddly cursed lol. I’ll finish it one day. I have to haha