Can you explain why? I also got platinum in Infamous 1+2 (and 3 now ) and I think this one is the best by a decent margin. It has problems (repetitive side-missions, less content), but the gameplay and powers are even better than in the predecessors imo.
And it just gets better with more powers unlocked.
I can tell that the game is good, it is beautiful and controls smoothly but as much as I loved the others one it just didn't grab me. It's definitely something wrong with me not the game. Maybe I'll give another shot down the road but I put in about 6 hours in three different sittings and it just felt like a chore every time.