Bad Airports:

BOS due to the poor layout and lack of a master plan. Also the attitude of the employees and security personnel including the State Police (How are they allowed access to automatic weapons?!?)

LGA because of the mentioned darkness and pigeon droppings. C'mon PANYNJ! DCA was a mess and yet it was fived up. You CAN do it. (Exception to LGA is the Marine Terminal used by DL Shuttle, I'm glad it has survived!)

JFK and EWR are more bearible than before. Both will be better when the JFK AirTrain starts up, and the EWR AirTrain/Monorail is finally made reliable.
(Tip: JFK is a ghost-town if you avoid the 2pm to 8pm window)

LHR is a pain to change at if you are changing terminals. As an arrival departure point, especially with Heathrow Express, I find it quite bearable even with the extreme security.

CDG2 is a pit with not enough area between the street and the gates for security and services/concessions/shopping. CDG1 is dated, dated, dated! Give me ORY!

SVO smells funny and really needs a steam cleaning. Thank goodness for DME.

I am biased, but LAX is OK for me. I avoid Terminal 1 due to the lengthy security lines that seem to exist at all times save evening. T3 is dingy, especially on the arrivals/baggage level. But as I tend to fly airlines with which I have club access, I guess I am able to avoid these things?
Delta's Termnal 5 is quite nice, IMHO.