I'm not too up on the AoS background, but basically there is no "planet" per se, as there used to be in the Old Warhammer (with the Empire, Lustria, Bretonnia etc.) It all got blown up. Now there are "realms", which are basically...kinda...planet-y things? I guess? Could be planes of existence. Doesn't really matter. What does matter is that each one is themed after one of the old schools of magic. e.g. the realm of beasts, the realm of metal, the realm of light, the realm of death, etc. These don't actually reflect the goodness or badness of the realm, as you get both good and bad peeps in all 8 realms. They're all linked by a number of basically magical tunnels called Realm gates. These could be actual gates, or something like a creepy old house in the woods, or a crack in a tree, or whatever. Humans exist in all 8 realms, and have differing ways of life depending on where they live. The realm of Light (Azyr) is inhibited by Sigmar (the god) and his Stormcast (=Sigmarines=reincarnated mighty warrior types from various realms.) The other realms have different rulers (eg I'm pretty sure Nagash is in the realm of Death.) Yes, some of the Big Names of the old warhammer survived the place being blown to bits by walking through a magical portal, so GW can trot them out again as needed. Interestingly, Slaanesh got captured by Tyrion and Teclis, and has been largely out of the picture, being supplanted in the Chaos Pantheon by the skaven god The Horned Rat. But Slaanesh is back again now, with lots of nice minis, so not to worry
Chaos has pretty much taken over all the realms except Azyr, to varying degrees, and now Sigmar is launching his great crusade from Azyr to restore peace and order to the realms. If this all sounds a bit 40kish, thats because it is.
Sooooo, onto Warcry.
Warcry is a skirmish game set in one of the realms I cant remember the name of where chaos warbands are gathering to fight for Archaon, bigbad chaos boss dude. Each warband in the game reflects its realm of origin - the beasty ones are from the realm of beasts, the kinda egyptian-ish looking ones are from the realm of light, the big meaty chaps are from the realm of metal, etc. There are also (helpfully) rules for several other non-chaos factions, because, hey, the good guys gotta go spy on the bad guys, and orcs just like a punch up. And GW would like people to buy more minis and not everyone likes Chaos cults
Rules-wise is where the game gets interesting. It's quite different to typical GW games, and does away completely with the usual M, WS, BS, S, T etc stats. I'm planning on a more complete write up of the game rules and general attractive points in the near future. Watch this space
For now, it looks pretty streamlined compared to typical GW games, with baked in stuff for scenario generation, warband improvement/campaigns, and so on. I'm keen to play, and have bought the rulebook and some cards (it uses cards for warband organisation, which really, really helps. They're not too pricey, either, which is a nice bonus.)