Ah...I don't know. The original Playstation had tons of great games. Parappa, Fear Effect, Resident Evil, Metal Gear Solid, Final Fantasy VII, DDR, Ape Escape....seriously, the list is long. It's longer than the N64's list, though the N64 has a better controller and, of course, Nintendo first-party games.
PS2 is the same way. By far the largest library of great games, in spite of being the weakest of the three available consoles (first to market, though, so that can be forgiven to some degree). PS2 has more great games that can't be had anywhere else than any of the others.
Personally, I don't own a PS2 and never will, as my primary concern was getting Nintendo 1st party games, so I got a Gamecube first. After than I ended up deciding on an Xbox on the strength of what could be accomplished with a mod chip and Xbox Media Center. But there are a lot of PS2 games that I'm looking forward to finally playing once I have a PS3 someday (definitely not at launch).
But for the average person who isn't going to take a soldering iron to the inside of their system and doesn't have an irrational loyalty to Nintendo, PS2 is clearly the best of the three systems. It simply has a far larger library of great games than Xbox or Gamecube. And what else matters?