Paycheck didn't really impress me. Good premise, promising beginning, but it kind of bogs down about halfway through. Various characters make various dumb decisions; the chase scenes aren't terribly exciting; it's fine, but nothing special.
It reminded me in some ways of a computer adventure game: you have a set of objects in your inventory, and each of them has a specific purpose, and when you get stuck you examine your inventory to see whether any of the objects seems likely to be useful in solving the puzzle at hand. It's all clever, all fits together nicely (except for the climactic scene, which doesn't really seem to me to fit with what we've been led to expect), but it's engaging more as a set of puzzles than as a story. For me, anyway.
This is another case where I more or less agree with Roger Ebert's review:
Paycheck begins with a thought-provoking idea from Philip K. Dick, exploits it for its action and plot potential, but never really develops it. By the end, the film seems to have lost enthusiasm for itself.... Because the director is John Woo, we expect a chase and a martial-arts sequence, and we get them, but they're strangely detached; they feel like exercises, not exuberations.
Side note: There's an FBI agent in the film who I was certain was Matt Damon doing an uncredited cameo. Turns out in fact it was Michael C. Hall; I recognized him because he plays David on Six Feet Under. He has a vague passing resemblance to Damon, and because it was a Ben Affleck movie I mis-recognized him. Also funny: John Woo originally wanted Damon for the lead in this movie, but he says Damon was "unavailable"; something on the Net indicates that Damon turned it down 'cause the role was too similar to his role in The Bourne Identity.
I've liked Affleck quite a bit in various movies, but I think I like Damon better these days. In these action-movie parts (except Sum of All Fears), Affleck sometimes seems to me not to have a lot of character for some reason.