First and foremost is simple - beautiful hair. He's got the hair you wish you had when you were dreaming that you could be a model or a movie star. It makes for great pictures. It also isn't soccer. Marc Burch as a soccer player does some pretty good things and some things that aren't so good for a left back, which might be why he ended the year being more of a left mid.
In the attack he's got a slow to fire but pretty accurate cross. Since he gets forward a lot from the left back position that can be a nice addition to an attack, but it also works from the defensive side of the field as a long switch. He's not great at short passes or triangles. On dead balls Burch can be the one taking the kick, always with the left foot.
Defensively is where things get more questionable, and probably the reason he is no longer a Sounder. Marc is adequate in positional defense, only OK 1-on-1, but significantly lacking the speed to make up a misplay. This is hard when as a LB he can be the last line of defense. As a midfielder it is less of an issue.
This may just all be a way of saying that Marc's a decent backup left mid and slightly less good backup left back. All together that's probably a better player for a team that has a clearly awesome left back and a team that doesn't really use wide left mids (that Brown guy practically being a forward).
Burch should be a solid enough defensive sub and occasional starter and unlike the rest of the Re-Entry Draft players does not come at an absurd price.