Yeah, I know that RE4 technically came out on the PS2 & Wii as well, but much later, and it was a pretty iconic GameCube game.
And yeah, for all that the PS2 is great, it weirdly kind of lacked an A-List headliner "you must buy this system for this game" title, like Halo was for XBox or SoulCalibur was for the Dreamcast. The next runners up for a broad-consensus PS2 title are probably something like Shadow of the Colossus, Metal Gear Solid 3, Final Fantasy X, and other flavors of GTA3. Longshots being God of War, Silent Hill 2, ICO, and the cross-platform Okami. And all of the above have issues - SotC is a tad too arthouse, MGS3 has backlash from MGS2 combined with lower sales than MGS2 despite being awesome, FFX doesn't quite have unanimous support among RPG fans (some people hated the voice-acting and characters, even if they're wrong), etc. Of course this really shouldn't matter as at least some of these should be able to matchup to the likes of Fallout 3, but whatever. (Also insert usual sigh that Fallout 3, not New Vegas, is the one that gets the nod.)
So what's the Elf list of favorite Mario games post-64, then, filtered for public consumption (e.g. would recommend to a random gamer rather than personal favorite)? From the critics, SMG1 was right on the bubble, actually, but the next Mario game after that was SNES Super Mario Kart I believe, although it was notably a bit below the bubble (7 points when 9-10 are needed). After that the Smash games which sort of count, and after that it gets really misty. I personally haven't played enough recent Mario games to say if the critical opinion is rational or not - I played uh New Super Mario Bros. DS, and that's about it. (and these best-of lists seem to have huge amounts of portable disrespect for some reason.)