I saw the movie yesterday. I went in, knowing it was not going to be as serious as I might expect it to be, and expecting it to be bad.
In the end, I thought it was a decent movie. Not fantastic, but it could have been a LOT worse. If you're a fan of the books, I'd say it's worth seeing at least once, just for the experience. I was very pleased that the movie stuck quite close to the book (for most things). I do wish Alice and the rest of the Cullens could have had a bit more in-depth introduction and role in the movie. I thought the humour in the movie was just fine too, though if I had went into it expecting it to not be funny at all, I may have felt differently.
The books were definitely still better, and they go way more into the details of the "Twilight vampire" lifestyle than the movie does.