Caution: giant wall of texts regarding Vita and a couple of games.
The Vita is a nice piece of kit, though I'm taking some time to get used to it. I have a personal issue where I try not to hold the device like a PSP due to the back panel, even on games where it isn't used by the game, so then my hands get a bit cramped. But the analog sticks are nice, the right side buttons are a bit smaller than usual, but still work well, and the D-Pad is amazing with its responsiveness.
The 2 games I currently have are Lumines and Touch my Katamari.
Lumines is still the great game if you enjoyed the PSP ones (I only played the first), song selections are good for my tastes and the skins are wonderful as ever. The only issue I had (very minor) was that the time trials didn't allow your to restart/replay, you always had to finish it or quit, so it loads back into the menu, then you select the trial again and another loading into the game again. Touchscreen controls in this game is pretty bad, and there's no reason to use it. You can also tap the back panel to boost up your meter for your power (dependent on what avatar you choose), the intention was to encourage users to tap to the rhythm of the game, but usually I'm too focused on what my move is to do the tapping.
Touch my Katamari is a great portable game due to the stages being timed, so it's easy to just pick a stage you know you can complete by the time you need to stop (say to get off at a station). My friend watching said the draw distance on objects were bad, but playing it myself I get too focused on the foreground that I barely notice it. The problem I had with this game was some of the controls, where to do a speed roll you had to do 2x full circles outwards (left:anti, right:clockwise) but is way too awkward to use for me. The touch screen controls fairly well, and is great for maneuvering around obstacles in tight areas, but not so great for just speeding around the maps, of which there aren't too many, but enough to keep you coming back.