I think Greenwood is a great choice: He's played the role of a leader very effectively in the past and he looks close enough for purposes of the film and considering Pike is not someone hard core fans will go nuts over if the actor doesn't look like his twin brother. Speaking of the fans, one thing that has been pointed out is that Captain Robert April was actually the first commander of the original Enterprise, not Captain Pike. I don't know if Abrams and crew will just change that for purposes of the film, gloss over it or what. Personally it's not that big a deal to me.
Filming on Star Trek began yesterday and the film is slated to open on Christmas Day 2008.
Source: Latino Review