i played mission 1 so far, it took about 30-40 mins but you spend a lot of time scanning big empty areas looking for collectibles (since you won't be able to replay missions for a while, just restart game). Its fine. Nothing great, nothing terrible. It reminded me a lot of Gears of War 5, gruff characters and enemies who love to monologue with giant big spaces to shoot around in. Combat felt really good and satisfying, although its weird that its generally better (on console anyways) to NOT ADS since auto-aim is pretty strong.
I'm pretty sure 3-4 hours is if you rush rush rush and don't stop, I've seen 10 hours is the more realistic play through and probably what it will take me. Which is reasonable, the original Halo 1 was 10-12 hours for a run. COD, Battlefield, etc are all around that time for single player campaigns. The visuals look great but then again so did Gears of War 5.
Is it worth $60-70? hell no. Its decent enough for a gamepass game, and I still really enjoy the multiplayer. Zero problems or issues playing. Its not gonna rank up there with God of War or Doom 2016 but when i compare it to TLOU2 or Battlefield 2042 (lol) or Halo 5 its pretty fun so far.