I finished the game yesterday and in my opinion this game feels like a dumbed down handheld version of the Batman Arkham series. I usually dislike this term and have played a lot of handheld spin-offs over the last two years (Uncharted GA, LBP, Assassins Creed: L, CoD BO: D, Killzone: M).
The change of gameplay from full 3D to 2.5D accounted partly for this. Even though I was disappointed that the Vita won't get a real Batman Arkham game, I personally like the 2.5D metroidvania style and was really looking forward to this game.
My biggest gripe with the gameplay is their weird pseudo 3D leveldesign. It made the exploration more complicated and I never learned my way around the world. I constantly had to look on the map, which thanks to the 3D leveldesign didn't really help me that much. The only time I liked the idea was at a predator encounter, which happened once in the whole game, what a missed opportunity.
I am sure that if they would have kept the gameplay to a classical 2D plane, maybe with a little bit background stuff, I would have enjoyed the game more. Ironically, this even more dumbed down gameplay probably wouldn't have let me feel like this game was a dumbed down handheld game because it didn't try so hard to be like the console experience.
It still is a solid game and I had some fun with it. Among those other spin-offs, I would rank it besides AC: L. There are many better handheld games to spent money on.
To spare you reading and myself writing a wall of text:
+Overall presentation works well.
+Graphics are nice.
+Many hidden goodies to find.
+Gameplay got much better with more gadgets...
-...after a slow start. Overall there weren't enough good puzzles/exploration with those gadgets.
-Weird pseudo 3D leveldesign with a slow loading and complicated map.
-In your face 3D presentation with bad camera perspectives in some encounters.
-Boss encounters aren't well designed.
-Combat wasn't varied and boring because there weren't enough enemies.
-Not enough interesting predator sequences.
-Vita's input abilities not used (no touchscreen on map, no backtouch detective mode).
-Bad playtime lengthening endgame.
-Minor bugs (game crashed, beaten enemies clip through the ground).