If you're a fan of fighting games, Soul Calibur II and III are certainly worth picking up (SCIII for the custom character creation system alone), and if you're into the whole MK series (which I am), then MK: Deception and MK: Armageddon are solid fighters (the latter has better models though and a custom character creation system, some of the character models in Deception look like they have sticks shoved up their asses). Also, if you like platformers, MK: Shaolin Monks is pretty decent, but a bit easy for a hardcore platform gamer. If you're looking for some retro action, there's a Genesis collection for the PS2 that includes a lot of different games, such as Altered Beast, Sonic, Comix Zone, and a whole bunch of other ones.
The PS2 seems to be largely devoid of decent traditional RPGs, at least over here. Such a shame.
