Of course, 3D platformers were really 3D exploration games, plonking you in non-linear worlds full of secrets, collectibles, and probably lots of talking animals. For one reason or another, the genre fell out of favour, but a few games are aiming to bring it back: Yooka Laylee, A Hat In Time, and now Poi. PolyKid's Poi is a "3D adventure platformer throwback to the 90s era of classic platforming games. Explore big worlds, compete in challenge levels, meet quirky characters and pull off classic platforming feats on a journey to become a Master Explorer". Sounds alright, that.
Poi is now on Steam Early Access, with 33% off if you pick it up in the next few days. There are two worlds included in this build, and a work-in-progress version of the hub world, plus two playable characters, and 18 thing-a-majiggers ('explorer medallions') to collect. Personally, I only really consider Early Access for procedurally generated games like roguelikes—when the world is fixed, I'd rather go through it once, when the game's been finished. But I can't deny the allure of Poi's colourful, skyborn universe.
