I have basically the same story as you. I got a £20 PSN voucher for xmas and after reading a lot of reviews i was very unsure about getting it but i caved in and hoped that my £15 would give me some enjoyment.
So far i have only played episode 1 and i have to say i was suprised, i actually enjoyed it. I thought the graphics were reasonable and the characters interesting however the one thing that stopped me enjoying it were the massive slow downs i experienced when the action got a bit hectic, and occasionaly froze on me for a few seconds
Will the framerate be improved on PS3? Because it ruins it, i really enjoyed the story and gameplay but the slow down and freezing ruined the experience during the important moments.