I'm glad "Skin of Evil" is getting some love. It's one of my favorite episodes from season one. Although not perfect, I actually like the character of Tasha Yar and seeing her go in such a gut-wrenching way always gets me. Armus is a great, great villain who you actually feel somewhat sorry for in the end. As someone mentioned upthread, this is also one of the episode where Troi really works as a character. I love the scenes with her talking to Armus in the shuttlecraft. Plus, this episodes has great music by Ron Jones. I particularly like the long suite at Tasha's funeral, but the "action" cues are also very memorable.
All in all, "Skin of Evil" is just one of those episode I will probably never get tired of watching.