Is it possible that this game is causing a small memory leak or something? The performance seems to be fine, but then progressively gets worse and worse and eventually crashes. Then if you do a full reboot, the performance is decent again. (it really sucks when it crashes after you finally get to 150 anarchy...)
I haven't noticed any progressively worse performance, but I'm in the same boat. It'll freeze after a decent chunk of time (I've noticed it seems to happen most often when multiple assets are pulled up at the same time, i.e. opening a vendor menu, trying to immediately select an item, and the vendor owner audio clip playing), then I say bye-bye to all of my anarchy.
As for the reviews, I've only read the IGN review, and it was pure garbage. Outside of Sanctuary and a few isolated areas, the framerate holds at a solid 30fps. I'm having 0 problems with the touchpad on the Vita slim (and my long fingers are typically always hitting something on the back but not here).
My only gripe is that characters' dialogue when they contact you via radio is often delayed, playing 2-4 seconds after their picture pops upon on the screen. It's not all the time, but it can make conversation between multiple characters unnecessarily drawn out.
Compared to most, I'm relatively new to Borderlands. I only started the first game a month or two ago, and at the moment I'm sitting at level 25 with the Soldier (I haven't played in weeks though). I'm loving this game, but I'm also very curious to see what the differences will be when I transfer my character over. I'd highly recommend this game to any Vita owner.