"Sometimes a bit of difficulty can add a lot of replayability, but as of right now there are issues and bugs we've encountered in development that are making it far more difficult than intended," Back 4 Blood developers Turtle Rock Studios have said. The Left 4 Dead-style monster-mashing has become notably more difficult following the big November update, with undesireable consequences, and they laid out plans to remedy it.
"Difficulty needs to be our 'baby bear' in Back 4 Blood's Goldilocks story. It needs to be 'just right,'" Turtle Rock said in a Reddit post. We want it tense. We want it challenging. We want you barely squeaking into the saferoom with a horde hot on your heels and you feeling that rush. We do not want it unmanageable. We do not want it to be unfair. That is our mission. Players must have agency. They must win and lose, prevail or perish, by their own actions. Skill, planning, and teamwork should carry the day. That's the goal. Part of reaching that goal is finding the right balance -- just right -- through constant adjustment to the various card systems, spawning systems, AI director, and other facets that affect gameplay."
The post details some of the causes and solutions. So yes, they had fixed a bug which made Special zombies spawn too often, and then they discovered another cause and plan to fix that. They note that the game had a problem with Trauma damage being dealt too quickly, which they have already fixed for online play with a server-side patch but offline players will need to wait for a downloadable patch. But they do defend the nerf to melee cards, saying "we believe these balance changes better the game."
Also on the subject of playstyles, they acknowledge that "speedrunning seems to currently be the most viable method for higher difficulties" and it can be frustrating to get matchmade into a team where one player builds for speedrunning then ditches everyone. "We don't want that to happen," they say, noting they plan to address it "in future patches."
Their post has more info on individual issues and plans, if you want it.
Turtle Rock recently laid out their content roadmap. By the end of this year they plan to have added new cards and solo offline play with campaign progression, a holiday event, and other bits and pieces. Then next they'll add a new co-op mode and start getting those paid expansions rolling.
They're building on firm foundations. Alice Bee says Back 4 Blood "is so much fun".