The Rifts system is horribly, awfully broken. Step 1 is asking the GM what house rules are in effect and what classes and such are allowed. That is usually step one, but to make Rifts playable every GM I know basically made up rules as they went along because they were necessary.
Its fun. And with a good GM is perfectly fine to play. But you really need to talk to them first. When I ran it I didn't allow Dragons, Juicers, and Crazies for a variety of reasons but would at least entertain most of the other things.