Why is season 11 so underrated? I think the high-quality writing completely returned, and the season has some great well written and well acted episodes. In my opinion, seasons 9 and 10 had a few great episodes against many mediocre (or even bad) ones, season 11 had a majority of episodes I think of as top quality, with maybe 5 mediocre ones.

My favorites:

A Man, A Plan, and A Gal: Julia
The Doctor Is Out
The Placeholder
High Holidays
The Ann Who Came To Dinner
Caught In The Act
Boo!
Miss Right Now

The great:

No Sex Please, We're Skittish
The Babysitter
Maris Returns [1]
Murder Most Maris [2]
Guns N' Neuroses
Match Game
Crock Tales
11.23 Goodnight, Seattle [1]
11.24 Goodnight, Seattle [2]

The average :

And Frasier Makes Three
Sea Bee Jeebies
Detour
I'm Listening
Coots and Ladders

The no so favorites:

Frasier-Lite
Freudian Sleep

Anyway... just my 2 cents. I think a lot of people see the Daphne/Niles thing as the start of the decline, but I don't. I think it unfortunately coincided with the departure of a lot of the better writers, and I think season 11 proved a series can evolve and not lose it's way.