Thumbs-Up:

DTW - home airport, new modern clean terminal for NW, tram makes it quick to get from end to end, parking in the deck is extremely close, tons of e-ticket kiosks to check-in
HNL - its in Hawaii, open air, very laid back
SLC - rental car area inside deck across from terminal, short walking distance, good airport for a mid-sized city, close to the city & mountains, easy in/out of airport
CLT - decent for connections, gets the job done well
DCA - close to the city, easy access to public transit, nice terminal

So-So:
DEN - nice airport, but takes a lot of time to get out of the airport from when you get off the plane (train to terminal, super long waits for baggage, long time to get rental cars)
DFW - had several good experiences, several bad - depends if there are t-storms around
ORD - great if the weather is good, bad if it is not, too delay-prone
MSP - some areas are nice, concourse F is a mess and overcrowed, can take a while to make connections

Thumbs-Down:
PHL - if there is a cloud anywhere in PA, PHL will have at least a hour delay, 4 if there is fog. Stupid Concourse F Express set-up that is detached from the rest of the place.
ATL - need I say more
RSW - extremely overcrowded, I'm sure it will be great when the new terminal opens