I've been to:
Old Foxboro - benches were crappy and cold (and a problem for a woman smushed between a bunch of guys bundled up for the winter), but being close the to field was great.
Gillette - seats are more comfortable, but fans are too far away from the field, affecting crowd noise and ability to see the game; also even though it looks good on tv, it's not really that nice a stadium; still a dim concrete block without enough bathrooms underneath.
Superdome, NO - old stadium that was falling down in 2001, but site lines were still good even from up in the rafters (we sat 3 rows from the top on the goal line where Ty Law ran it in for the TD).
Reliant Stadium, Houston - the best NFL stadium I have been to; bright, plenty of bathrooms and concessions; even sold wine and mixed drinks (these things are important to us girls). Got stuffy when they closed the roof because of the threat of rain.
Giants Stadium/Meadowlands - another old stadium, but they have seats and crowd is close to the field. They let the kids come right up to the field/players before the game.
RCA Dome/Colts Stadium - old with metal benches in the upper deck where I sat. Got incredibly loud. The thing I liked about it was its location. Picture putting Gillette in the middle of Fanueil Hall - lots of bars and restaurants; no need to tailgate outside (unless you wanted to).
Ralph Wilson Stadium, Buffalo - again an old stadium (metal benches w/ backs were I sat); most like the old Foxboro Stadium; liked the "feel" of the game here.
My overall impression of these stadiums is, although the newer ones offer you a more comfortable seat, you give up being close to the action. There is nothing like a good football game in an old stadium where the crowd is sitting (or screaming) close. Too bad they couldn't just add a row of corporate boxes to the top of the old places so they could get their revenues and we fans could get our football experiences!
Edit - Went to Alltel too; not equipped to handle a full capacity crowd; bathrooms didn't work on one side of stadium and concessions ran out of food