I liked it personally and thought it was great game play, and thought the sleeper mechanic would be an "addition to" what we already had, instead of the sleeper mechanic taking it all over, for ever building.
I was hoping it would be like: You made noise outside to try and wake them up, and the majority of zombies would try to get out like 60-70%, and the rest (30-40%) wouldn't activate yet till you started to cross the trigger points. So that way you never truly knew if the building was totally cleared or not, and still needed to proceed with caution.
The path finding is at a point now, that they would be able to path find, over just destroying everything, no matter what level of the building they were on. Even if, some did go the destroy route, then no big deal. Next time stealth your way in instead.
No biggie though, it can be done with what they have. Just not worth the effort, till they are done. Too many building to go through and set up, just to have it be changed later by them.
Edit: Just my opinion ofc. TFP will do, what they are going to do. Not expecting them to change things, just on how I would like it.