They will film the second season over a ten year period following all the actors in real time following their characters as they grow older. The story is more sprawling and grand and takes all different kinds of paths as the kids grow up, Hob does his shady stuff for the government and Joyce deals with the repercussions of what's happening to Will. It mixes the strangeness of it all as they advance through the 80's following real life events as well as the fictional story line that spans the US and other dimensions. We watch the actors and their characters actually age and deal with the mundane issues all kinds of crazy shit happens as well with things slowly building and building. You release that long awaited season ten years later and boom, epic story telling, literally.
Then the third season is like the second half of Stephen Kind's It where the kids are all grown up, Hobb is even more burnt out but for more Lovecraftian reasons, Will is on the run from the government and 11 returns from the Upside Down like Connor did in Angel (the show) but actually bad ass after all those years training, honing her powers and surviving the terrors of the Upside Down. Its 1993 it all comes full circle as Dr Brenner shockingly returns chasing after 11 all these years later but he's different now. Something happened to him after the monster dragged him there a decade ago and now he is a force of nature acting like the Tall Man from Phantasm and bringing all manner of surreal and terrifying horrors with him to destroy humanity. The characters all set a crash course to huge climax as they confront the ultimate evil and finish what was started so long ago.