First off is the plot of the movie itself. It flows smoothly with the musical numbers actually being a part of the plot; enhancing it, without stopping any of the action, which is the sign of a good latter-day musical. The only flaw in this section is that it's all too short. There wasn't any time to show any of the characters' growth (or in some cases, downfall), but seeing the events unfold will definitely capture the imagination.
Most important is the performances: Jamie Foxx does a fantastic job of acting and singing; it may not be Oscar-worthy, but he definitely didn't phone this performance in. The dubious nature of his character makes it difficult for the viewer to want to either side with him, or despise him.
Beyonce shows immense potential as an actress. While her character is obviously based on Diana Ross, Beyonce takes the role and makes it her own. It will be interesting to see what she puts forth in the future.
Most people my age will remember that a long time ago, Eddie Murphy made a record album. While we tend to make fun of it nowadays, his performance is nothing to laugh at. He makes the most out of his character who wants yet another shot to be at the top again (perhaps a parallel for his career?).
Last, but definitely not least, is Jennifer Hudson. Now, I'm proud to say that I've never watched an episode of American Idol, and I didn't hear until after I've seen it that Ms. Hudson lost somewhere close to the end. That being said, she definitely doesn't sound like a loser to me. She takes her role and gives it everything she's got, which goes to show that Simon Cowell is not the end-all be-all when it comes to talent.
The set design and camera-work is nothing to behold, it's very straightforward, but there is nothing that distracts from the overall product either.
Overall, this is a movie that's worth paying full-price admission to, highly recommended!