1. Gravity Rush - Don't listen to the reviews on this one, absolutely fantastic game. Free with PS Plus.
2. Little Big Planet - Having a full fledged LBP on a handheld is amazing.
3. Persona 4 Golden - Port of the greatest JRPG ever made.
4. Metal Gear Solid HD Collection - Two of the best MGS games on a handheld, not much more needs to be said.
5. Tearaway - I haven't played it but I've heard many good things. Media Molecule has yet to disappoint.

You must hold the vita vertically in your left hand(left stick top,right stick down)

Than use your left thumb to constantly press the virtual ?" button"

By pressing the ? the game shows you always the next possible move.That's a lot easier to build up combos & bonus mulitpl.,makes fun and makes you usually score 500k without problems.Levelling up to level 70 is pretty easy and you don't need to pay a cent for the f2p shit.You don't need to use any jewells before level 20-25.

When adding the totems & the other stuff(using jewels) like dynamite etc this game gets a lot better than tetris or puzzle bobble.Than it is really really addicting.

(edit:this is how it works when you are right handed and move the stones with your right hand.You can't do this while holding the vita the usuall way the your left hand will always collide with the right hand)

Just 5 games it too cruel! I guess just retail-wise I'd say:

Persona 4: The Golden
Killzone: Mercenary
Tearaway
WRC4 (yeah It's now become my favourite portable racer)
Little Big Planet

Though this will probably change every time you ask me!