I already played mg2 I thought it was really <cough> great getting to play mgs again. I would have been really pissed had I not returned the game.
As far as games I like
RPG
FIGHTING
platfomers so so usually too easy
GUN GAMES ARE GOOD
MUSIC Games frequency and guitaroman
Lemme see what I can come up with for ya:
RPG - I tend not to play these, so I won't comment.
Fighting - You've probabyl already played Soul Calibur 2 and Mortal Kombat: Deadly alliance for the Xbox, so my picks for the PS2 would have to be Guilty Gear XX, Tekken 4 (or Tag, they're both cheap), and the upcoming King of Fighters double pack.
Platformers - If you don't want easy, try Maximo (and it's sequel), or Contra: Shattered soldier. They both reach back to the good ol days of difficulty. Me, I like my platformers a little easier, like the Ratchet and Clank games or the Jak and Daxter games. You might alos give ICO a try, it's more puzzle than action, and surprisingly good.
Gun Games - With a Guncon 2, the Time Crisis games are fun, and I'd reach back into the PS1 catalog and recommend the Point Blank series as well.
Music - You've already listed Frequency and Gitaroo Man, there's always Amplitude (Frequency 2), and you can pick up Mad Maestro for dirt cheap. The DDR games are good, and the EyeToy: Groove is very similar to Samba de Amigo for the Dreamcast. On the rhythm side there's the re-release of Space Channel 5 (With SC5-2, for $15), and PaRappa.