The atmosphere was great, you definitely accomplished a lot with sound and the mood and pacing were fairly consistent. The shock value moments wore off after I started anticipating them but I did get a good jump off the first one, you had me paying attention to the text and it sort of came out of nowhere, which was a great bit of misdirection.
The graphics lacked consistency, there was a lot of detail in the wall textures and the paintings but not so much in many of the objects, and the lighting and shading seemed to vary wildly from item to item - also the main character's sprite's hair flips back and forth on highlights while he walks, that's a very simple thing to fix just by copy-pasting his head across. In general the tileset needs a lot of refinement but that's not such a big deal, and fortunately when you do some refining you can apply it retroactively to older chapters as long as you don't rearrange. :D
I did dig the creepy paintings though, I don't know where you managed to find some of them but they worked great. A little more variety would be nice though, I don't imagine even a crazy creepy old uncle would have the same four paintings duplicated so often throughout a house.
Also the mid basement floors, I'm not sure what you were going for with the walls, metallic or what, but they just didn't come across right, really just off looking.
The mapping was decent, it didn't quite accomplish anything that I would call a consistent layout of a house but it go the point across. Lots of pointless objects and clutter were present that didn't really seem to add to it, crates and cabinets all over the place that didn't really add atmosphere or contribute in any way to gameplay. There were quite a few pathing bugs, nothing game breaking but I discovered in multiple areas I could walk into walls, over the sides of the staircase entrance, etc. I would take a closer look at your passability and priority setup, it seems to me like you have some passable objects sitting on higher layers than impassable objects that you are layering over, resulting in non-blocking walls. I'm sorry I didn't make a more thorough note of where I ran into them, I wasn't really in beta-testing mode at the time, but I believe the biggest one was in one of the rooms directly after the basement around the area of the cannon ball trap, where I walked several tiles into the wall and was able to wander around a bit (may have been the stable). Like I said, wasn't game breaking, but definitely needs polish. :D
Oh another little bug was the trick hallway between the upper floors and the basement where you have to take a left through an unseen path indicated by inconsistency in the carpet: the two different halls used to pull off the trick are 1 square off from eachother so there's an awkward flipping effect when you go from one to the other. It would be a much smoother transition and thus better effect if you quickly fixed that up.
The traps were simple enough that I picked up their patterns pretty quickly but I died a couple times in learning so I think the balance was right on there. Puzzles in general were very simple and straightforward, they reminded me of the old adventure games where you just sort of wander around looking at things till you find the right object to click on, then wander around more until you find the right spot to put it - nostalgic in a way, not innovative but at least for me not stale either.
Oh back to the traps, I found myself suiciding a couple times to work my way backward (it turned out to be unnecessary) but you might want to keep track of what direction the player approached from when he moves into a set of traps. Same goes for the torch rooms where you could choose to "go back" if you were out of torches, I actually entered the basement from the far side, forgot I was out of torches, and got spit back out into the hallway on the west entrance.
A few thematic inconsistencies: In your introduction you note that the location is Antarctica, but then refer to the house as being built "up there", which read sort of weird, I was thinking, am I actually in the Arctic then, or am I up in some mountains in Antarctica, or whuh?. Also, it's "We treasure hunters" not "us treasure hunters" :D Um, other than that, the big long mine-shaft like hallway in the basement that leads to the locked door you can't get through, when the lights go out there's a clearly electric sound effect where you mention earlier in the game that all the lighting in the house is gas, unless that's an intentional inconsistency it came across weird, especially since the light on the wall is a torch. The sputtering sound from the fire traps would probably work just fine.
Oh yeah one last thing, where in the world did you get that crazy Shoggoth on the roof song? It was awesome.