I recently saw this movie in the comfort and privacy of my own home. The music instantly had me hooked. It's bright, energetic and infectious, and expertly woven into all levels of the story: stage performances of the group, "story songs" ala the tunes in a musical, and some pieces that were straight opera, with the dialogue and conflict sung. (I believe the term is "rock opera" here.) Many of these clips stemmed from or wove into rehearsal scenes, stage reprises, progress montages, radio announcements ... skillful integration of awesome music.
As far as the story itself, the last part of the movie slowed almost to the point of drifting interest and could have been truncated without losing any of the impact, but it was otherwise an engrossing storyline. What struck me the most was the fact that no character was completely in the right throughout. A series of partway wrong decisions created all the misfortunes, and you still sympathized with (most of) the characters despite them.
The performances were fantastic. I can definitely see both supporting act(or/ess) Oscar nominations (I'm indecisive about Hudson's win still), though this is definitely a movie where main and supporting blurs. Hudson's voice is shatteringly powerful, but what really impressed me was Beyonce's range. She managed to "tone down" when singing the stage-sets a character who was supposed to have a fairly unexceptional voice, and then ripped out for a few of the opera/story songs mentioned above.
(Mild spoilers below.)
Dreamgirls' story arc is best summed up by the two songs that are both, at pivotal points in the story, repackaged by another singer. These songs represent taking something raw and vibrant and commercializing it. It's particularly striking in the second set of songs, where one simple word-choice completely alters the meaning of the song. In the original (this song is performed, not story), the singer expresses her wish to love a man, but "you really don't have the time." In the recap, it becomes, "I really don't have the time." One little pronoun and a very striking expression of regret becomes bubbly, and the rest of the song thematics follow.