Why does everyone hate Onslaught arc (XMen)?

Just as the title says, why does everyone hate the Onslaught arc of X Men comics?

It was a pretty '90s story. I was still pretty young at the time, not even into my teens, so of course I enjoyed it back then. But it's not really a great story, and there are a lot of pretty shitty elements to it.

Those who wrote it had no idea at all of what to do with it when they started writing it. Literally. They didn't even know what kind of villain would they end up using.

That gives you an idea of how badly plotted the whole thing was.

That seems to be a surprisingly common running theme to Marvel's writing "strategies" during the 90s.

Case in point: Judas Traveller.

So the problem was the actual plotting of the story?

The Onslaught arc was actually when I started reading comics, so I had somewhat of an unbiased opinion when I first began.

In theory, it was a good concept: a villain gets hyped up over a long course of books and does quite a number of previously-thought impossible feats (such as hurting the Juggernaut) that just up the ante. When I first happened upon the idea, I was stoked. I didn't really read Marvel at the time, but something that epic just felt like something I needed to witness.

Unfortunately, the plot just didn't have substance. Even being a total comics n00b at the time, I recognized that. Onslaught was a Generic Doomsday Villain with no real motivations besides "becoming a god". Right from the start, even, we're given no reason to care about him because he is quote-unquote "The manifestation of all Professor X's evil", which is the cheapest possible origin you can give a villain.

The only part of the Onslaught arc I ever read was the trade paperback for issue 3. I remember wondering what was going to happen next, but I got the feeling that there was no way Onslaught could win.

Put simply, the product didn't match the buildup.