I'm a moderate X-Men fan (I won't buy it if it sucks), and I don't even get it. My guess is that Professor X was just making everyone think he looked like a huge fucking monster and their ultimate foe is really just a guy in a floating wheelchair.
There's a difference between Onslaught and Infinity Gauntlet, though. Infinity Gauntlet was a nice self-contained miniseries that doesn't require any previous reading to get.
Onlsaught, however, does not get that luxury. It all takes place within issues of a bunch of ongoing series, resulting in a crossover that is essentially all tie-in books with no actual crossover miniseries to tie into, except for two bookends. And it was probably tailored to make way for "Heroes Reborn." It's all just so poorly concieved.
