I've gotten a few games of AoS in so far, and our results have been.... interesting.
The mechanics in general make for a fast game. We all had fun, as well. This is -not- Warhammer '9th edition'. In fact, it's best to simply think of it as a completely new game.
But the game has a couple HUGE flaws.
First - no army building rules. You can take whatever you want - even mix figures from different factions. You can also take as -many- as one thing as you want (on most warscrolls. Some do limit you to a single model). Want 100 Chaos Warriors? Go for it!
Second - Summoning is outrageous, and tons of armies have the ability to do it. The generic Chaos Lord, for example... every turn he can roll a d6 - on a 4+, he can call in reinforcements - one of various units with a certain tag. Yep, Chaos Knights and Chaos Warriors are on that list. AND,that unit can be as big as you want. The one game I saw him in, the guy failed the roll on turns 1-3, but made it roll on turn 4-5. POOF, virtually another entire army appears. Heck, I saw where one of the Lords of Change can summon... another Lord of Change! Ugh.
That being said, GW reps have mentioned that in the coming months, there will be 'force construction guidelines' coming out. Right now it's a virtual free-for-all as they wanted people to 'get used to' the new rules, as it's a pretty monumental change from their usual game standards.
The group I played with... they're non-munchkins, so we all agreed on certain number of models max, and a certain number of wounds max, and eliminating summoning altogether. Doing that... we actually had a fabulous time.
The biggest boon is - the rules and the army lists are free. You can use your current figs just fine. So really, you are only investing an hour or two to try it. But right now, trying it will likely give you a negative feeling, I am afraid.
My group still holds out hope that GW will get stuff rolling to the point where this game can be salvaged before it crashes and burns fresh from the womb!