This game is awesome!!
The PC version is only $29 so the Mac version will be the same. The console version is $39 but it's still an ok price. This game is wonderful. I downloaded the demo and played it on my PC and it played like a dream.
After you complete a level you have a 'free-play' mode where you can change into different characters and walk around. It's fun being an enemy droid and sneaking past the bad guys without them knowing.
If you haven't seen screenshots or the trailer for the game I say you should look at them before you judge the game itself. At first I didn't know what to think, but after looking at the screenshots and videos I downloaded the demo right away! Heck I even submitted this story and reserved a copy of the game myself!
Game Info, Screenshots, and Trailers:
http://www.legostarwarsthevideogame.com/flash/player.cfm
http://www.lego.com/eng/starwars/videogame/default.asp
I can't wait to play the full version tomorrow.
EDIT: Here's a screen from 3Dgamers.com, yeah it looks much better when all the settings are on high though: