The steam reviews are mixed, compared to overwhelmingly positive for L4D2. It's also Windows exclusive with Easy Anti-Cheat so it can't run on Linux. (It's a coop game, who cares about cheating there??)
I haven't played it, but this video gives the impression that it is much less polished in comparison to its predecessors. However it could just be nitpicking.
https://www.youtube.com/watch?v=EdRLNUGmFC8
I would recommend giving this video a watch. It'll show you just how much care and attention to detail was put into L4D 1 and 2: https://www.youtube.com/watch?v=EdRLNUGmFC8
It's okay. The difficulty ramp-up is really steep to the point where once you finish the easier difficulties it just gets way too hard. Maybe if you play with friends it would be different, but I was mostly solo queueing.
That being said... it was a lot of fun until I got frustrated with it! It's on the PC game pass.