Generally, I liked it.
Was it great? No.
Was it good? Yes.
The visuals were stunning and they did a fantastic job of emulating the classic Steve Ditko style in the backgrounds. Unfortunately, most of the best moments were shown in the trailers. The same is true of the jokes. There is a lot of humor in this movie and sometimes the movie goes for jokes at times it would have been better to play the drama straight.
The script does a good job of retelling Stephen Strange's origins from the comics. As some have noted, Strange seems a lot like a magical Tony Stark and in terms of backstory that's a fair comparison - an arrogant jerk is humbled by an injury and unwittingly becomes a hero while trying to save himself. The difference in the comics came later, with Strange attaining true humility and Stark being... well, Stark. Time will tell if the same thing happens in the films.
The cast is excellent, though I think Rachel McAdams is completely wasted here as the love interest. Nobody is really challenging themselves as an actor or breaking any new ground, with Benedict Cumberbatch playing an American Sherlock Holmes (see the above comment on arrogant jerks) and Chiwetel Ejiofor basically playing Baron Mordo as the order-minded Operative from Serenity. Benedict Wong steals every scene he is in as bad-ass librarian Wong and Tilda Swinton has the appropriate gravitas for The Ancient One.
One thing that did occur to me regarding Swinton's casting as The Ancient One and the resulting outcry over Hollywood white-washing Asian characters. Acknowledging that the "white man goes to the East and becomes The Chosen One" trope is highly overdone and that there is a case to be made for trying to eliminate the equally cliched stereotype of The Wise Old Master by casting a woman in that role, I wonder why I haven't heard any similar complaints about Baron Mordo - Doctor Strange's arch-enemy, who was Transylvanian in the comics - being cast with a black actor?
All controversy aside, I would recommend seeing this movie on the big screen. And be sure to stick around through the credits for two special sequences.