the only thing about crystal city is that is kind of shuts down after the office crowd leaves. a few of the restuarants there along crystal drive have a bit of a night life and yeah there's pentagon city mall...but old town (where king street metro is located) definitely provides more options.
the gaylord seems nice -- been there once for a conference -- but there's nothing around it to walk to...it's pretty isolated. no metro access. i've heard they're supposed to get a good water taxi service this spring to make connections to old town and downtown d.c. better...if that happens it would be a prety cool option.
edit: actually found a link for the water taxi. it starts march 1:
http://www.potomacriverboatco.com/newtaxi.php