It plays exactly like the original flash version, just it doesn't save any scores or have any online scoreboard support.
+: Great port of the game, it has all the levels in it and everything plays the same. Even music.
+: Still very challenging, especially near the end of levels.
+: Controls are also great, despite no mouse.
+: You can play Vector TD on the go.
-: NOTHING new compared to the original.
-: Doesn't save scores, doesn't have online scoreboards unlike the original.
-: Original is free.
-: Music can get insanely annoying after a while.
-: Hardly takes advantage of the PSPs graphics.
You just have to decide if this game is good enough to bring with you on the go or not, and if the no saving whatsoever flaw is not drastic enough to get in the way.
And yes really there's not much else to say, play the original if you want to try it out.