We know, it's just the fact that SAO makes a lot of basic storytelling mistakes and is quite the high profile production just aggravates the public. It's not just some shovelware shit brewed up in someones basement, like your The Room's and Birdemic's. It had an actual studio, with a big budget, working on it, and basically anything you need to make a pretty dank anime. And it was trash. Besides, it got incredibly popular in the (relative) mainstream, despite being shit, while great shows (if I'm not mistaken either Jojo and/or Madoka premiered the same year as SAO, and got nowhere near the recognition) struggled to make a blip on the radar, and that just aggravates us even more (think Twilight, for example).

TL;DR: It's high profile, expensive trash, which just makes it worse.

Here, check out Mother's Basement.
This first video has little to nothing to do with story, but is nonetheless quite interesting:

The following video, however, has everything to do with story. It's equally interesting, and points out exactly why SAO sucks:

Personally, I've never seen the anime. However, after hearing people mention how bad it is, I found the above two videos to explain things pretty well. And, as someone who plans on writing stories as a career, I must say that Jeff's analysis is pretty great.