I saw this movie today (opened yesterday here) and was simply delighted.
I saw a review that said something to the effect that the reviewer thought this would be just another teen movie, but then found it was based on Shakespeare's Twelfth Night ... and then started trying to justify liking this flick on Shakespearean grounds. I really think this is going way overboard: the only connections I could see with Twelfth Night are (a) the basic conceit of a girl masquerading as a man; (b) the extensive male-female humor arising out of that basic conceit; and (c) some of the names (including Viola & Duke).
Aside from those names, the thematic commonalties (a & b) are really great themes for any script, and this movie's script is no exception. Beyond that, though, this really is a simply delightful and very contemporary/traditional teen flick. And that's a perfectly legit genre even if highbrows have to find an excuse to like it ... like alluding to Shakespeare.
The movie is bright, fast-paced, emotive, stylized, funny ... full of teen hormones and teen humor and male/female humor suitable for all ages. And that's really the best part IMHO: really just about every male stereotype and every female stereotype is depicted in roundly appealing over-the-top fun. Those stereotypes are parodied relentlessly but affectionately, with such a complexity of invention that I'm still a little bewildered ... but really don't feel at all disappointed in that regard, it's not that kind of a movie: things come at you fast and fun and you get a laugh and a groan and then move on to the next split-second happening.
Amanda Bynes really is just delightful as Viola / Sebastian; Channing Tatum makes a wonderful Duke; David Cross does a wonderfully over the top Principal Gold. All of the acting and characterizations were fine and on target. Cinematography was excellent.
Wonderful entertainment from beginning to end ... check it out!