Varies for each character mostly. My latest character I haven't bothered to get Spellbreaker, Atronach Stone, or any sort of magic resistance, so he gets GraqeD by magic. However, my wizard character laughs at magic users, but archers can be trouble (usually can lock them down too, but if one gets a sneaky shot off, it can HURT).
Can't remember the name. It's a cave in the Reach where bandits are living, but a horde of Falmer invaded. In the front room, there's like 6-7 high-tier Falmer (Gloomlurker, Nightstalker, etc.) vs. a single bandit. It's the highest concentration of Falmer I've ever seen in one room - nay, the highest concentration of any enemy except low-level draugr. That fight is unbelievably frustrating. The only notable loot from the dungeon is a warhammer that swings faster than normal.
Yeah I know where you're talking about. Evil, since the Falmers have a pretty rounded mix of enemy types (melee, archers, magic). If you just keep the high ground, stick behind a pillar, and Fos Ro Dah them when they rush up the stairs, you can manage.