Koenig, as you probably don't recall, was one of Nick Fury's Howling Commandoes in the comics, who started as a Nazi, joined original non-Sam Jackson Nick Fury in World War II, helped form SHIELD, and was still an active agent until his extremely recent death. Also, he was a tall, muscular blond, so casting Oswalt is a very... interesting choice. That said, I can't see how the addition of Oswalt in any capacity isn't going to be great for the show.
In Marvel's announcement, Oswalt has a lot of good things to say about the series — really specific, detailed things, so I think he probably means it. Still, here's the interview's highlight:
As a fan of the series, Oswalt has been asking the question many have posed, namely "Who is the Clairvoyant?"
"When they first told me the character's name, I'll admit the first thing I did is I went on Wikipedia and looked up the M.O.D.O.K. character to see if Koenig was maybe his name before he became M.O.D.O.K., but it wasn't," laughs Oswalt. "They keep on talking about the Clairvoyant in the show and I'm like, 'is that M.O.D.O.K.? Am I M.O.D.O.K.?"
However much Agents of SHIELD continues to improve, I guarantee whatever the show has planned for the Clairvoyant won't be nearly as wonderful as the idea of Patton Oswalt as M.O.D.O.K.