...my personal opinion...
i bought the x2's played with them a few hours and so pissed my ears were numb. took them back b/c i saw the x3's coming out. now i have the x3's, played with them a bit last night and thought they were pretty nice. here's my ramble:
-sit "on" your ears, not "over" so your ears literally go numb
-took a while to turn on or sync to station
-station big and bulky, supposed to be a docking station but i never used it
-battery compartment weird design, have to bend cover to get in place
-ir transmission, if disrupted, makes horrible sound/hiss
x3's: (new to these but here's my assessment)
-thankfully these sit "over" my ears
-i wouldn't say extremely comfortable but they're nice and reasonable
(i'm 6'4 235lbs, gotta pretty big noggin and my ears weren't hurting at all)
-IR transmitter WAY!! smaller than the x2's, nice suction/velcro for attaching
-noticed their voice technology which raises voice levels during intense times
-what i really noticed is how horrible other people's mics sound... geez
-weird at first but i now like their technology that allows you to hear yourself
somewhat through the headphones.
-expanded feature works... nothing amazing but it works
-bass boost sounds nice. def. helps
-wish it was made it black
-button config on headphones takes getting used to, (fumble around for a while)
-nice mic clarity
-no annoying static when disruption of ir transmission, just goes quiet (at least so far)
all in all i'm happy. i realized there are better sounding headphones out there but for xbox live compatibility this works out nice. i was looking at the tritton one's, which probably sound better, but turned away b/c i enjoy being as wireless as possible.
hope this helps!