Dungeon Master is not you vs them.

I some times feel when I am gaming that the players see the game as players vs. Dungeon Master. This is not how I want to look at it. My NPCs do not gain Experience as times goes on. I get no reward if they do well or have vast amounts of wealth. Lately Torrin has been not leaving any survivors to allow that any way.
Now I do trying and make it challenging to make the players actually have to come out of the “BOX” to solve the problem. Last Monday my players did just that. A group of NPCS where given the order to go to the other door and attack them from the other side. Torrin was holding the front line down from entering the room. So Ambrose with a brief poke and hint from Torrin went to spike the door closed. After a bit of discussion, I made Ambrose roll every round to hit the spike to drive it in enough to keep the door closed. Then seven seconds and 14 rolls later, Ambrose had two spikes holding the door secure. I think it played better than: turn 1 ok you spike the right side of the door. Ok turn 2 you get a new spike. And so on. I just want to get rid of them vs.me and put in, here is the situation now re act to it. Does any one out there have some good pointers on that line.