I thought the second half of the series in particular was so bad that I just couldn't finish watching SAO, but I can see why it's so popular. I probably would love the series as well would I still be 16 years old.
But I am not. And that's the bottom line. Kids like "stupid" things all the time. No reason to get angry about it.
According to bits of info from publishers (thru twitter, blogs, 2ch etc) there's no longer a market for characters that have to train to become stronger. Seems the audience either doesn't want to try, or doesn't want to be reminded of the times when they tried but never improved as much as the miracle protagonists in comics and light novels. So you end up with protagonists that start out in God Mode, get the girls for no good reason, etc. Supposedly, in comics where they still do that 'train to be stronger' thing readership drops noticeably during that period.
This is why SAO, despite appearing to be incredibly stupid, sells well -- it's just the trend. Just like the way OreImo pioneered longass, awful sentence-titles... because it boosts sales.