I gave it a "B," and that was being generous. It was enjoyable, but ultimately forgettable. I doubt I'll have any desire to pick it up on DVD.
The "love conquers all" and "free will vs determinism" (or destiny) themes are as old as fiction itself, and the film didn't really bring anything new or thought-provoking to the table, which is what I had hoped for when I saw the trailers (I had never read the Dick story, but I'm a huge fan of his otherwise).
Much of it is essentially a standard chase movie if the chases had taken place in the hallway full of doors in The Matrix and the Agents were more polite and all dressed like Philip Marlowe, except for the ones that were needlessly dressed up like Gestapo motorcycle gang-inspired random movie henchmen even though they were meant to go sight unseen, not to intimidate people.
Matt Damon really seems to take the world shattering revelation told to him early in the film in stride. You'd think it would destroy your entire worldview and seriously mess you up psychologically, but apparently it's just another speedbump on the road to love for Matt.
The performances were good all around, and there were a lot of recognizable character actors and real life political commentators playing themselves (Jon Stewart appears twice). Terrance Stamp was doing his best stoic but menacing routine. Emily Blunt was charming and quirky.
If you have a girlfriend who's not into scifi/fantasy (this could go either way) but always likes a good love story, this would be the film to try and get her to see. The instant attraction between Damon and Blunt - given in brief doses over years though it may be - is believable, and they make a compelling and likable couple who you want to win the day in the end.
Overall, despite the good love story and performances, the film itself is basically a middling quality Twilight Zone episode given a big budget and feature length. If you don't expect too much, you can enjoy it in that sense. But don't expect it to be profound or mind-blowing, because it's not, and doesn't even really attempt to explore the implications of its own premise.