to me, its not really a matter of what games u might play on the ps2 as it is a matter of your financial situation. you'll always be able to find at least some games u like on any platform, so its a matter of is it worth the money
i originally got a ps2 on launch date, and eventually got an xbox after it came out. but i quickly came to realize that buying games and hardware for two platforms (well, actually more like 3 since i have my pc) is waaay too expensive. several months ago i decided to start focusing solely on games for my xbox, and even though there have been games out for the ps2 that i wanted, not buying them has saved me quite a bit of money.
i just realized that i don't HAVE TO own every single good game out there... the good games for the xbox are more than enough to occupy my time (and my income). plus, if u buy a ps2, its more expensive than you think. chances are you're going to need a second controller, and you're most likely going to need 2 (or at least one) memory card, and if u wanna play with a lot of friends you're going to need 2 more controllers and a multitap, and if u want to play online you're going to need the network adapter, etc, etc...
so, in short, i wouldn't recommend getting a ps2 if you already have other console(s). the only exception to this is if you're a die-hard rpg fan, because no other console has the rpg selection of ps2.
and as far as the reverse situation (buying an xbox if u already have a ps2), the same thing applies... it depends on your financial situation. the only differences are that the xbox is primarily an fps/action console (as opposed to having a lot of rpgs) and, imo, the xbox is a much better console than the ps2. i could get into why, but i don't really want to start an argument or a flame war or anything. u can message me if u really want to know my opinion.