1) No team is guaranteed super-ultra unbeatable. They might look the part during the season, said team beats everyone in the regular season on both sides of the ball, and then the media hypes up said team(s), and then said team(s) look very beatable. Call it injured key players, bad calls, no calls, whatever you want, but some teams had the shit scared out of themselves last night.
2) Say what you want about the teams that didn't "belong" in the playoff. You think another team should have been in the CFP. Well, that team didn't do what needed to be done to get there. Who else belonged there besides Georgia? Who else would have survived Georgia's schedule and gone undefeated? Michigan shouldn't have been there? Name a team that would have come back from that many down to at least make it close. Especially facing the Heisman runner-up. And with that many no-calls by the refs or badly reviewed calls. Ohio State shouldn't have been there? You saw what they did last night, right? No other team has done that to Georgia (in Georgia's backyard) this season. TCU shouldn't have been there? You saw what they did to Michigan's run game. What other team would have put up 35 points in the second half against Michigan?
3) Those were two fine CFP games. We have had blowouts before, and people were unhappy. Now, we have two close games, and people are unhappy. Say there was too much offense? Well, I think offensive schemes have a one-up on defenses these days, especially teams that can throw and have great receivers. We have seen great defenses in the past give up a ton of yards. A couple of years ago or so, Alabama gave up a ton of yards and points to Kiffin's Ole Miss team. I feel like stopping the run is pretty good for some teams, but the passing is very difficult to stop.
4) I never played a down of organized football in my life, but I feel that cornerback has to be the toughest position to play. Watch out for the WR or TE breaking, going for an out route, adjusting to an underthrown ball, having your back turned in man coverage, and the mobile QB takes off, getting your head around to go after a pass, etc.