I saw Jarhead last Wednesday. It was a very good flick, definitely worth seeing in the theatre. It made great use of the kinds of cinematic effects that lose their punch when viewed in your living room: sharp cuts from silence to thumping music (quality soundtrack overall), occasional overwhelming sound of gunfire (although surprisingly little for a war movie) and large, sweeping onscreen vistas.
Jake Gyllenhaal, Jamie Foxx and Peter Sarsgaard all turn in top shelf acting performances. You definitely get the feeling (and this has been said about the film in many places) that the writer throws in all kinds of Corps myths in this one company. Pretty much every "I heard there was this one guy who..." story happens to these few guys, which is a little unbelievable, but not so much that it detracts from enjoyment of the film.