First one (title screen) is fairly awesome, but I'm curious why the title is in English but the commands are in Spanish. Are you mid translation or something?
Second is definitely nice. Only thing bothering me is how the grammar sounds, but it's believable for a first person narrative type.
Third one starts to cut to the meat of the game. Right off the bat I notice that the main character's sprite is of a completely different style than that of the zombies, and it is rather distracting. The room feels a bit... crowded on one side and empty everywhere else, and it's kinda unbelievable for a real library. I would suggest spacing your stuff out some more, adding a bit more detail in between, that sort of thing. Pretty much ask yourself if this was your own personal library and you were standing in it, how would you set it up?
I absolutely LOVE the lighting and shadows that you've got there. I don't think I've ever seen that sort of set up before, I'm gonna have to PM you sometime to ask what sort of script you used for it. However, I do notice that it also effects your HUD up there in the corner. It's pretty dark in a lot of the screenshots, and that's not a good thing. Is that fixable?
Fourth screenshot. I like the right side, save for the legs of the stools seeming to stand out more than they should. I like the left side, save for the pinball machines being a bit too bright. But that middle... did you use like a wall tile around the carpeting? And a portrait on the velvet rope? Hrm.
Fifth screenshot. The floor seems to really change a lot. Think you can clear the clutter by just using one piece across all of it? Another thing, you've got what looks like a keypad hanging above the door there. Looks good for a light, but feels a bit strange with the buttons and whatnot there. Similarly, the white keypad is way too high for the character to reach. I'd suggest either editing the tileset or copying it over to a new sprite and manipulating it so that it'll look to be between the two tiles.
Sixth. Whoa. Chaos on the floor there. Okay, you see how a lot of the tiles look to have a small portion of a grate? That's because they actually form a sort of line to put up against walls. The ones that take up a half tile are the main ones, while the ones that take a quarter are used to connect it when it turns. Play with it a bit and you'll see. Not too much else to say, except that I like the water there and that I think you've got the back of the computer's lighting up instead of the front.
Next one seems pretty good, though something's obviously off with the light effect on the bookshelf. I think you've also got a picture half hidden behind the elevator door.
TO BE CONTINUED! Maybe. If I don't forget or pass out after dinner.