You know, I used to share your opinion on not being able to get into anything that wasn't Mario. Then I played Kirby.
Kirby's about the most similar thing you could get to Mario. It's primarily a platformer with all sorts of different spinoffs, the main four characters are about as ironically wacky as you could get, and the gameplay, while significantly easier, is also a lot more varied due to the Copy Ability system. And while it doesn't actively focus on story, there's actually some pretty dark lore hidden in the final bosses and side modes. I'd definitely recommend it.
1: Super Mario 64 is one of the worst mainline Mario games.
2: And so is Super Mario Sunshine
3: New Super Mario Bros. is the most criminally underrated game of all time.
4: Super Mario 3D Land deserves more praise. It's not as bad as most people say it to be.
5: Super Mario 3D World, on the other hand, could have been much better. I hate cats, and who was the Sprixie Princess in the first place?
1. The original may not have aged the best but I stand by the opinion that the DS version is excellent.
2. Eh, you're not the only one. I really enjoyed Sunshine but it did have some pretty serious flaws.
3. NSMB is very underrated but there are a few games I'd consider even more underrated (like, well, the entire Kirby franchise).
4. 3D Land was easily the 3D Mario I enjoyed the least but I still liked it quite a bit. People really exaggerate how bad it is.
5. As someone who really liked 3D World...you really could have chosen bigger flaws to dislike it for.