If Mike Gibson was definitively better than Stacy Andrews, we could say "wooo! better line." But Gibson is not definitively better than Andrews. So what should we expect?
Inferior pass blocking
Andrews is no stone wall, but he benefits quite a bit from being enormous. He doesn't get bull rushed back too often. Instead defenders separate and gap him left or right. That isn't good either of course but compare his pass blocking to, say, Max Unger. One kills you in spurts (Andrews). The other is a continual weakness (Unger). Unger wasn't beat that often, but man did that guy ever live in his own backfield.
A continual weakness creates two specific more recognizable problems: no pocket to step into and blitz expressways.
Improved run blocking
Remember how Alex Gibbs unexpectedly retired a week before the start of the regular season? How that same day it was announced that Seattle had traded for Stacy Andrews? And how deductively there was nothing to prove it was anything but a coincidence but inductively it seemed fishy?
Well Andrews is not a through-and-through bad run-blocking guard. He's big. He's powerful as hell. And he moves surprisingly well. But the guy's not a technician and he's nowhere near quick enough to be an effective zone blocking lineman--at least not in pretty damn pure ZBS.
Gibson is a little bit quicker and a little bit better in space and that might help transform this
but I wouldn't count on it.
Anyway, something had to be done and Mike Gibson must be doing something to earn coach after coach's respect*, so I can't really complain. We will see if it makes a difference. We will see if it lasts four quarters.
*My money's on excellence in gritbagitude.