I just finished beating the boss in Dead City, and went through the hospital lobby, up the escalator, and then there's a hallway with an elevator at the end. To the left is a room with a door that has a small window in it. Through the window I can see the room with the defib upgrade, but I cannot open the door, it just shows a red 'x' when I approach it. I cannot proceed at all, I am completely stuck. I'm really starting to regret buying this game.

I have run into this exact problem. I watched a video on you tube and the door opened as soon as the player entered the room.

In the comments it mentioned that this glitch occurs if you take to long to kill the giant mutant.

I haven't had a chance to reload an old save prior to killing the mutant yet and probably won't for a couple of days.

Have a go at killing him quicker and let me know how yo go.

I don't think it has to do anything with how fast you kill the giant mutant.
It took me quite a bit of time to beat it (had to figure out the right timing to shoot the rockets, if the timing wasn't perfect the shots wouldn't register) and the door was open for me.

I Reloaded a seved game and the door just opened, not sure what caused the glitch but happy to move on now.

I got the defib upgrade by accident. I was exploring the hospital and a door just opened. I walked in and picked up the item on the table. I haven't experienced any bugs at all so far.

is this glitch gonna be patched because i still have the same problem

Past the door with the head in front.

I Try to pass the closed door. I run through it an press the x. After a minute it happens. The screen swiched in to a new situation and i can go on.

hi,the door just don′t open,this game is a disgrace.
i never seen in one game so many bug′s,but this one is just the bigest of them all.

what a disappointment.

i start the game,i kill the boss slowly,quickly,a lot of saves after and before,and nothing.
a new game and it′s trash.
i never going to bye more games from this publisher.