Why do so many people hate aatrox?

Because he is an inherently toxic champion that will either be too strong and annoying or too weak and useless. Right now he is useless, and usually a guranteed loss.

http://na.leagueoflegends.com/en/news/community/q/ask-riot-trust-question-and-aatrox

What are your thoughts on Aatrox? He feels like he is in a horrible state and could use some buffs or a rework.

We'd like to do some significant work on Aatrox when we do a class update to diving fighters. Aatrox has a theme with an enormous amount of potential. At present, however, his gameplay is a bit generic, doing a mix of things plenty of other fighters also do. That means, unless he's the best at those things, he's not going to be the best pick gameplay wise. Our goal with an update, as a result, would be to make him more unique, taking advantage of his backstory and letting him bring some distinct tools to a team. We'd also like to do some work before then, both to help him out slightly (he's a little on the weak side) and at least start to push him in a more focused direction. At a rough guess, sometime around the pre-season is when we'll likely look at that.

I haven't played much either but I think he's not bad. I don't understand either.

To some people, none of his moves give him that feeling of power like other fighters. He can be strong but he feels item-reliant unlike Nasus, Garen, Darius, etc who can just build tank and have a ton of damage. Tbh, you can go tank and trade with W and still deal a lot of damage.

You need positioning, you need to make sure your bloodwell is full for maximum attack speed and passive recovery, you need to know tricks like trading when W is ready or hitting teams with your ultimate to fill the well faster, or building tanky items rather than glass cannon, you need to know that your E is a short cd ( 6.4 sec cd at rank 5 with 20% cdr from ) almost 3 second slow and you can use to escape or chase enemies, you need to know that damage does more for him than attack speed. You need to know the reason his E even does magic damage is so they can't build armor and completely null you. But a lot of 1st time players just think of him like a weaker Xin and rush then complain when it doesn't work.

Coming from a former Aatrox main, he is basically a lifestealing cannon minion.

there is a champ named aatrox?

He's a decent toplaner, just not cream-of-the-crop as far as the toplane roster goes. Most of the flak he gets is directed toward people who play him as a jungler since he has nothing to offer in terms of ganking that the next champ couldn't do 2x better, and falls of quickly if he doesn't get a laners' income to get items up quickly for midgame scraps.

I like taking him top, though. With the right pages I can stay in lane from lv.1 all the way to the point that I can afford a gunblade rush, maxing E first and basically winning any trade against all but the most ferocious toplane bullies. So many people who complain about Aatrox here seem to have the preconceived notion that if you're not buying Bork and maxing W first then you're not doing it right, but he has quite a strong magic-based poke in his kit, synergizes really well with Thunderlords for more burst, and makes EXCELLENT mileage out of Gunblade+Rageblade for a sweet mixed-damage build.

He doesn't do anything well enough and the passive is annoying to play against.

No one understands us, they call our work a hackjob.