As to the tile appearing crooked, sometimes there is no much you can do if the walls are out of square.

The dark spots look to me like when the tiles we cut the backing chipped out.

We have a lot glass tile projects and our installer cuts the tiles by scoring and snapping. They always score the back first. This will prevent the chip outs on the back.

Get a hold of a level and check the lines yourself to see if the grout lines are level. They should be level whether your house is crooked or not. I have heard that cutting glass tile is difficult and personally have stayed away from it for that reason. There are lots of "how to" tile websites on line. You Tube has some great one's too. I can't see the whole job, but in my opinion, there should have been better planning to avoid that skinny tile in the corner. The whole job could have been shifted right or left 1/2 a tile to make those skinny tiles larger and the ones next to it more of 1/2 of a tile. While you're researching, you can find out whether it's standard practice to use a wet saw on glass tile (is that what he did?) or if the snapping method is what is recommended. I recall when reading about the sheets of small glass tiles for back splashes that they recommended using "nippers" to clip off the edge if it was too long.

Thank you Frank! I'm thinking of asking them to re-do the tile in the corners so that it doesn't have those dark spots, and I'll ask if they can score and snap to prevent the chip outs

Thanks chromatic! Those are all good considerations, I'll talk to my husband and contractor about them.