I saw it opening day and was very impressed. Sure, it wasn't ground-breakingly original, earth-shatteringly well acted, or awe-inspiringly meaningful, but it was a good movie nonetheless.
As for those who make a huge deal about Ashton; just fucking get over it already. Yes, he normally plays non-serious roles and yes, he seems to be a teenybopper favorite, but he does just fine in this movie*. Just forget about the actors themselves and focus on the story in which their characters are participating and you'll be ok.
Oh, and the movie is very dark..in a mainstream movie sort of way. There isn't really a sustained cheery moment anywhere in the movie. The end my be a little too Hollywoodish for some, but I it was far from "Yay! Everything's fixed let's all dance a happy dance" happy; I would call it bittersweet.
In conclusion, go see it. It won't change your life, but it will make for an interesting couple of hours.
*Except for when he runs. Kutcher, in my opinion, has always looked goofy when he is running. Serious movie or not, Ashton running gets a smile from me.