Old Aatrox worked around auto attacks. This took away a large amount of the skill expression a lot of people wanted to see in a "swordmaster's" kit.
The new Aatrox has a higher skill cap, but is also a lot more rewarding when you actually hit them.
If you played Triforce Aatrox at any point and liked it I'd say you'll enjoy the new one more. If you preferred just pressing Q E AA and hoping they died before you do then you'll prefer the old one.
On the whole I think the changes good. He does feel slow I'll warn you now, but I think that's more because with everyone saying things like "Riven 2.0" you have certain expectations on mobility that he just doesn't fulfill.
I think he's going to take some getting used to, but he'll be enjoyed by a LOT of players now, rather then just a few one tricks.