Marathon's gunplay is really really good and the team fight experience is excellent. Playing solos as a Rook is really fun too. Playing solo as a shell is fun but less universally appealing, solo games are more like arc raiders where you might not kill everyone. The problem is everything around that is bad. The game is fixable, they need to give up on it being an extraction shooter and turn it into a BR with larger team fight modes and dedicated pve content.
The issue is that they are bungie, and cynically thought if they have this cyclical extraction shooter game they don't have to make a full games' worth of content, maps and plot. Cannot believe they spent $200 million and this is all they got for it. ARC Raiders managed to have way more to engage with while coming in at a third of the price.