Pause the Action. Survey the World
For the most part Volume 2 of Onslaught: the Complete Epic is just filler. The first issue or two deal with the X-Men on their mission to deal with Onslaught. Reveals that Xavier is like Batman: crazy prepared! He has files on how to kill each of the X-Men. That was neat to see. The issue where Wovlerine talks to this Aboriginal mutant was pretty awesome. Esp the fact that such a guy exists. But the rest of the book just seemed like filler that could have been safely ignored.
That's not to say it wasn't fun to read. While the X-Factor story was boring and just involved the Beast/dark Beast story, the Spider-Man story was a lot of fun. The only thing that sucked is that it was still during the time of the clones so we had Parker and Reilly both instead of just Parker. The Green Goblin issue was great because it was the same events of the Spider-Man book from Goblin's point of view.
The X-Man and X-Force issues may or may not become relevant in future books.
The only thing that bugged me is that no one in the Marvel universe outside of the X-Men (and their affiliates) seems to know about the sentinels. Now, this may just be because I've only seen the sentinels in the X-Men 1994 cartoon where everyone knows about them. They appear on the news. Senator Kelley campaigns on using them, etc. I understand that heroes that aren't mutants might ignore it because the sentinels are after mutants, but they should still know what they are. Perhaps someone can help me out in the comments and let me know if this is a valid criticism or not.