The Geonosian Cannon set is relatively cheap. I think it is about worth its price for all the things it includes.
One thing I really like about this set, is that if you drop it, it won't completely shatter. Sure, a few small loose pieces will fall off, but the majority of it will stay together. Now, I've bought other Lego sets that I can't say the same for, and It can be very frustrating to repair them over and over again.
In this set come some pretty exclusive minifigures. None of these character you can get anywhere else. The Clone Wars version of Barris Offee is neat, as well as the Commander Gree and Geonosians. They are a great addition if you are a Minifig collector.