Gotta say the quest that starts in Darkfall cave and ends with getting the fancy bow is
IMO the best quest i have
ever done in an elder scrolls game.
What made it good for me was a combination of things:
I had to switch to torches to see in the Falmer Parts (i thought i already had candlelight

).
Also at low levels with fairly vanilla gear (was only
lvl 22 when i started it, albeit a very focused character (Block 75, One handed 80, Light armour 60*, resto 45 along with some one handed buffs)) Falmer are Pretty darn challenging. Their warriors are pretty handy with a shield and their bows do a tonne of damage. Was having to juggle my Arrow deflections, Vegetable soup fueled bashes/power attacks and Become ethereal-delayed fast heal (An indsipensable tactic for melee fighters, as long as you don get two-handed fisted you are practically invincible).
The Neato environment, the falmer canyon and glacial crevice felt really actioney and swashbuckling with all the narrow walkways and plunging cliffs.
The creepy atmosphere in the temple with all the frozen falmer.
Serana was a good companion, didnt steal any kills (looking at you Uthgerd the Unbroken

) but her ice spikes were really handy (mainly for making the falmer glow bright white in the dark
lol).
The only let down was the baby dragon duo fight was a tad easy.
*I Like to run fast okay! Also the jangling noise heavy armour makes really annoys me.