Don't forget good humor and brilliant character chemistry too. I think the actor choices are spot on. Baldwin and Buy More morons are funny as hell.

I even enjoyed Chuck's and Sarah's fake relationship antics. Seriously, this is one of the best tv-series I've seen.
Season 2 finale/Season 3
In the season 2 finale Chuck gets upgraded Intersect into his brain. Which apparently allows him to access pretty much any information, including kung-fu. I'm not sure whether this is good or bad. I enjoyed Chuck's character because he wasn't a super spy, he only had his smarts and the old spy-secrets-only-Intersect. But now I assume he can excel at close combat and firearms too whenever he needs to, which I'm afraid could destroy his character and make Sarah and Casey just sidekicks.