A few things here:
1. I LOVE Renner's casting. He single-handedly elevates Hawkeye to the main table. In the hands of a lesser actor, he'd be the worst kind of also-ran.
2. I HATE Ruffalo's casting. With apologies to Ruffalo, who is a fine actor and should handle the role well, Marvel just screwed the pooch on this one, plain and simple. Norton was willing to return to the role at a fraction of his normal pay rate, he'd already met with Joss to discuss JOSS'S ideas for Avengers (not his own) and he made it very well known that he was ready to work FOR Joss, not WITH him, and Norton's track record speaks well of his ability to work under a director he respects (Fight Club, anyone?). All of this invalidates Marvel's assertion that Norton would have brought trouble to the set. Aside from the Punisher, Marvel has fumbled the handling of Hulk worse than any character in their lexicon, a trend they've sadly chosen to continue here.
3. While I have my concerns about how well the Thor and Captain America characters will translate to the big screen, Marvel Films has shown dedication to an overall vision involving the Avengers characters in the Iron Man and Incredible Hulk films. They've handled certain potentially campy elements in all three films with a great deal of sincerity. Hopefully they'll present the Thor and Cap stories with the same sincerity and avoid too many cheesy/campy facets, allowing Joss and company to fold the stories into one cohesive (and potentially brilliant) Avengers film.
4. The assembled Avengers will bring to the screen a level of ensemble talent the likes of which hasn't been seen outside of an Ocean's movie, and NEVER in a comic book film. It's an exciting time and one thing's for sure: We're gonna see something memorable in 2012. It could be the absolute pinnacle of superhero films. Or it could be the most glorious trainwreck ever committed to celluloid. One way or another, we're gonna remember it...
5. Speaking of the Punisher, during this panel, Marvel Films's rep confirmed that they've reaquired the character and will be making the next Punisher film in-house. Hopefully we're in for a magnificent (and faithful) relaunch in the very near future!