I'm still waiting for my copy to arrive and it's something I'm looking forward to.
It uses the 5e chassis but doesn't strictly adhere to it. The 6 classes go up to level 5, then from 6 to 20 the game is classless. The default setting is the Alpha Base that gets established in the middle of Season 6, so much of the setting info is around that base and not the SGC. Playable species include the Tau'ri, Jaffa, Tok'ra, non-earth human offshoots, the Unas, and a new species.
It has a few other rules options that makes it more it's own game and not just a 5e clone.
Another thing I think is cool is you can buy the 3d print files for all the miniatures they are doing for this game, including a Stargate with a DHD.