I have the Final Cut production bundle, which includes Motion. I've played around with it a bit, mostly for motion graphics. Gun flares would be easy (you could even add smoke fairly easily) and I imagine bullet hits could also be done without too much fuss. Splattering brains may be a bit tougher, depending on what you have in mind and how much time you want to spend learning about particle systems.

All in all a good program, and although it doesn't even begin to compare with After Effects, it's much cheaper and easier to use.