Okay, so I don't approach this from a neutral perspective. Gus Johnson's name resides right next to "Pam Ward" in my book. The only question was whether he could completely ruin the Champions Liga for me, or whether it could be tolerable.
Lucky for Gus he had a pretty good, straight-up match to call (a 1-all draw between Real Madrid and Manchester United) without anything too confusing to expose his lack of knowledge.
But of course there isn't a single announcer from the UK (not even just limiting it to the English Premiership) who couldn't do a demonstrably better and more entertaining job than Gus Johsnon. He got it by default, essentially, because, as somebody said, there was no way in hell they'd ever get Joe Buck to do it.
I liked this wonderful paragraph from Deadspin:
I don't believe Johnson is distractingly bad, but there's something to be said for the fact that he brings nothing to a game. Think of all your favorite Gus Johnson moments: they're buzzer beaters, long touchdowns, incredible plays all. Johnson became famous for losing his cool when the moment called for it—but those are just moments. He's the ideal announcer for the morning after on Youtube, but not someone you want to spend three hours with.
The verdict after Gus Johnson's debut; it wasn't so bad that I had to turn the tv off. He may have actually benefitted from the viewing possibility that he'd screw up so badly, and there would be such a tremendous crack-up, that you wanted to be there, watching, when it happened. Like watching a NASCAR race.