Personally I love it- I was a big fan of 8th (7th was a little dull) and played it as much as I could- I much prefer Aos!
The balance is intuitive rather than based on arbitrary points values. Players use experience and discussion to create the game they want to and make it fair. There are additional rules which offer easier chances of victory if you're severely outnumbered, but the real balance comes from scenarios. AoS is made to run on scenarios rather than straight up pitched battle.
It's designed to scale really well- you can play with just a box of 20 guys and a Hero, or you can go all of the way up to 200 models if you like. Your army can be any size you like and organised in any way you wish. Plus you can mix and match units from different armies for theme and variety.
Despite what some say, it's not a skirmish game, that's not what the designers were making (from the horses mouth)- it's a mass battle game, same as it ever was, but it offers the opportunity to play smaller games too.
AoS is highly mobile- lots more movement and tactical maneuvering available than in 8th ed. It gives a much better representation of medieval warfare: you can have units of skirmishing archers at the front which then fall back through the lines of the swordsmen; ranked combat works excellently with different weapons having different ranges in combat- swordsmen at the front with lines of spearmen behind reaching through to attack.
Units can advance in block formation (using movement trays if you wish), before moving into a line, wedge or dragon-teeth formation for the combat.
A game or two in and AoS seems fairly simple- a dozen games in and you start to realise the tactical complexity involved. Playing AoS taxes my stratgic mind far more than 8th ed. ever did!
Because the game is scenario or discussion balanced, it makes pick up games a lot nicer. You don't have the issue of putting down 1500 points of themed army and then getting smashed by someone's tournie list in the name of point-balance. Turn out some models, play some games!
The fluff/background has progressed significantly since 8th ed. It's the same timeline, just eons into the future. The World-that-was has been destroyed and now the descendants of the Warhammer races and their gods live and fight across the 8 Mortal Realms. In fact, some of the heroes from the Warhammer World are now Gods...
AoS has gone very High Fantasy; realms created, fueled and filled with magic, Gods walking among mortals, Celestial, immortal Warriors...
As yet, we are still to discover a lot of what is happening and what the races have become- the releases are narrative- background is being revealed slowly across releases.
There are so many good things I can say about Age of Sigmar! As with everything in life, it's not going to be for everyone. But it's definitely worth giving it a shot and seeing what you think about it. And doing that is easier than ever seeing as all of the rules are free to download!
I'm about done I guess. I can't think of enough bad things to say about AoS, and would strongly encourage you to check out Mantic's Kings of War or something instead - if you like GW's (wonderful) miniatures you can use them in that system and keep playing something much closer to what Fantasy was. If all you really liked about Fantasy was the limited RPG elements though, and you had no interest in the setting, and you think you can find friends to play AoS with who have the same mindset as you, you can probably have some luck with it. If that's the case, more power to you.