Well I personally really like the Tesla's design. It looks more like an actual monster than a pig/human hybrid. Also I'm a sucker for blue electricity. I probably would have even liked the model more if it was a bit more mutated looking and larger... also maybe having blue slime dripping from its mouth. >
The "boss" Tesla encounter was the scariest part of the game (even if by "scariest" I mean on par with a DD encounter). I didn't get what I supposed to do right off the bat so ended up skulking around the perimeter. (btw, I went to the right after entering the room, and the switches were to the left whoops)
It was pretty tense. The first switch was easy enough, but the monster seems to be scripted to "warp" close to the second switch when you get within a certain distance to it. I barely managed to sneak past it and still got hit once right after throwing the second switch.
All in all it was pretty scary, but not exactly difficult. The only part I had difficulty with was figuring out what I was supposed to do in the lower piston room. It took forever to find that stupid coal chute. :/