Yeah I guess you could hold out on Re4, its coming for PC and should be better.
Anyways,
If you like GTA a lot, Liberty City Stories is there and Vice City Stories is coming in March.
Also, God Of War, then get God Of War 2.
Then either give God Hand or Devil May Cry games a hand, they are both very similar, but God Hand has a light and comedy atmosphere wheras DMC is serious. Both are extremely hard games even in their easiest mode.
Coming to RPG's, the list on th Ps2 will 'Never' end. Final Fantasy 12 alone should consume more than 60 hours of your life and it is a beautiful game. FFX and FFX-2 are superb. Play Okami as well, its on the same league as FF12.
If your RPG's are atill left craving, you can't miss Kingdom Hearts 1 and 2. By the time you finish these all, you'll most likely be an RPG addict, then get Star Ocean and all the games in 'The Tales Of....' series. And even the just released Rogue Galaxy has been getting killer reviews.
You can read up the reviews here :
Top PlayStation 2 Games - Best PlayStation 2 Video Games - Best PlayStation 2 Games - Top PlayStation 2 Video Games
Coming to other genres', Marvel vs Capcom 2 is a *must-have* if you like 2d fightin, also Street Fighter Third Strike is pretty much one of the most respected fighters alive today for its depth and is used in a lot of undergrounds gamers tournaments. Coming to 3D Beat-em ups, get Mortal Kombat Deception and Armageddon, Tekken 5 and Soul Calibur 2.
Coming to action/adventure, there's just plenty. Red Dead Revolver and Gun, Bully, Mercenaries, Metal Gear Solid 1 (psx), 2 and 3, Yakuza 1 and 2, The Getaway, Resident Evil Code : Veronica X , Marvel Ultimate Alliance and X-Men Legends 1 and 2, (though they come in Role Playing genre), Manhunt, Viewtiful Joe etc etc, there's enough to keep you busy for a year. For driving, check out GT4 and 3, Burnout series, and Midnight Club 3 : DE (if you think NFS Underground 2 was something, this game will blow you away), Tourist Trophy, lot of Nascar and WRC games you can try.