I've never played any of the other Borderlands console games, but just picked up Borderlands 2 for the PS Vita.
Absolutely loving it. For a handheld console game the graphics and gameplay are fantastic.
I've read that there are a few glitches so I don't know if they had already fixed them by the time it was released here.
I've noticed a little slow down when the screen gets busy, and some questionable AI with some enemies (after taking a shot at them, most will charge at you or roll for cover but some just walk in circles).
Minor niggles for a handheld game that looks and plays this good. The cel shaded graphics look great on the Vita and love all the little touches (like the day turning to night during play). And loved that you can engage almost anything. Took a few pot shots at the distant flying reptile things (figured they were just background) and was shocked when they suddenly flocked and attacked me.
Not without it's little problems, but if you've never played it before and you like RPG / FPS games it a must have for the PS Vita.