RTB is just a mod for v.0002
Difference between Retail and RTB, even though they can't really be compared, is that retail has no brick stretching, which is the biggest difference.
Other than that, Retail has great and improved graphics, more items, brick effects, better maps, and much more stable vehicles.
Retail also has a nifty minigame system, where several people can create different minigames, and the others can choose which one to join.
Over 800 people as of now bought Retail, which greatly overcomes RTB's community.
It's really worth it, and you don't want to miss out.