Basically you get all the classes, characters, starting zones, capital cities and teen zones for free. Considering you can’t unlock the last classes until level 13, this isn’t a huge amount to show. Still, it takes about 4 hours to get to 20 and the starting zones are pretty sweet.
If you haven’t played Rift, this is a great chance to try it. In my opinion, it’s the best MMO on the market right now.