I had a Gamecube so that's where my loyalties lie. XD But seriously though, Gamecube had an insane array of amazing local multiplayer games that people didn't know about (Pac Man Vs, LAN Mario Kart, heck even the Donkey Kongas) which made some of the most incredible gaming parties with my friends. I've never had the same with a PS2, or any other console for that matter (even Wii which was party game central).
Single player games were great too. SMS, WW, MP, TTYD, all amazing. Sure there weren't many third parties on board by why do you need them with exclusives like that?