I thought it was really good. Wasn't a huge fan of subbing in Cheadle for Howard, but the War Machine scenes were so good that it didn't matter. All the new stars were great, even if it seemed like Sam Rockwell's character was written to act exactly how Justin Theroux (who wrote the script) would play it. Great action scenes, plenty of funny dialogue, and a formidable stopgap movie while we await the Avengers...sweet Christ, I can't wait to see that movie.
I thought the Captain America shield joke was awesome, too.