Quite a bit different than what you named, but Jeanne d'Arc is probably the most addicting game I've played on the PSP yet...lol, I'll find myself playing it for 7-8 hours straight on weekends sometimes.

Disgaea is great on the PSP too.

I like Dungeon Siege: Throne of Agony too---sort of like a Baldur's Gate.

Crisis core is must own if your an RPG fan

MGS portable ops
Wipeout pulse
Loco rocco
GOW : chains of olympus (soon)
Silent Hill origins (also on PS2 eventually)

Syphon Filter: Dark Mirror of course. Just because i'm a syphon filter fan. I have the ps2 version but haven't played it yet. Sadly (but maybe not for you) i've read the psp version is alot better. If not dark mirror try syphon filter: logan's shadow.

Of those, I'd go for Metal Gear Solid. I would also pick up Castelvania: The Dracula X Chronicles. That looks really good.

If you buy a GTA game buy VCS ... its so exotic :P Also , buy Daxter , and the upcomming Patapon and God of War games :)

has anybody mentioned R&C game? Sure, it's not as great, but it's a must buy if you enjoy the console version.

I too throw my votes in for Jeanna D'Arc, a truly great game indeed.

Crisis Core and God of War in March. I'm so going to hype those 2 games.

good luck choosing whcih ever game you choose!! =D

If you can find it cheap you should pick up Guitaroo man also :P that game is so badass xD

if you want a MAJOR rpg killtime, pick up disgaia or FF Tactics: Lion wars :P

Lumines is damn awesome for a puzzle game, another time waster there,

Untold legends is good also if your into hack and slash RPG types.

For more shooting strategy PICK UP KILLZONE!!! That game is fantastic!

Oh and if you have a Memory stick, grab a bunch of demo's off the site :P

And I will agree with the norm here, MGS Portable Ops is GREAT :D 

Thanks for all the suggestions.

To let you guys know, for now I bought Syphon Filter: Logan's shadow.

Next time I buy a game I'll look back at this thread to see all your ideas again!