It's possible that Back 4 Blood could inherit some of Left 4 Dead's lack of rhythm. It can leave you with a rabid, frayed brain, something I felt in this early version of Back 4 Blood too. My biggest gripe with Left 4 Dead in retrospect is that you're shooting almost constantly from beginning to end, with only a saferoom finish line there to supply a moment of pacing. Sudden 'crescendos' of action felt tedious.
Will Left 4 Dead actually hold up well as a style of game in 2021? When I replayed that aforementioned community update in September, it surprised me how poorly some aspects of the shooter had aged. After playing the imminent alpha for a few hours, one question I'm left with is how many new ideas Back 4 Blood will need to be a great, fresh experience.