I won't make a comment on FATAL since I haven't actually seen the game, only heard about it- but it sounds like a real stinker.
Synnibar however, I have seen. Its simply the most assanine game I have ever seen, and the worst part is that the guy who wrote it didn't intend it as a joke. I picked up a copy for $5 at a local game store after hearing about it, just to see how bad it is. You know what? $5 is overpaying for it.
RIFTS is also pretty abysmal. While some of the ideas and concepts in RIFTS are cool, the system falls flat on its face. There are huge power disparity levels between characters and classes, and the system is a nightmare to keep up with during play. Pretty much true of all Palladium games, but RIFTS is the worst of the batch.
MERP/Rolemaster (aka Chartmaster) have high learning curves, and unless the GM is familiar with the system, they can be pretty painful. That said, MERP/Rolemaster are really good for more realistic games, but combat does tend to bog down. I like the feel of those systems, but its hard to see past the tables and computations when you play them, which to me kills the ability to get into character.