We didn't get to see it opening weekend, or even opening week. Even so, I was a pit surprised when we arrived at the theatre 10 minutes before showtime to see this:
Including us, there were probably half a dozen people in the theatre by showtime.
Another thing that was surprising: the Marvel Studios splash at the beginning was all movie clips, with no comics. Looks like Marvel is trying to stand on its reputation as a movie studio rather than a provider of comics. Which is a bit sad, since all of the movies are rooted, at least vaguely, in comics, and it seems a shame not to at least acknowledge that.
Anyways, the movie gets up your nose really quick with the "this is magic, take it or leave it" and as long as you buy into that as a premise you'll do fine. Stephen Strange gets on my nerves a bit, this movie does have a bit of the "beating a dead horse" thing going on when it comes to Strange's (lack of) acceptance of the mystical. Everyone says this is one of the best Marvel movies ever -- I wouldn't go that far, but it's definitely top half.