Anyways, back on topic, the only time the silliness really grates that badly on me is all the pop culture references. Things like "Care for a salad? I made it myself!" and "Hands Free to Victory" don't bother me as much because I actually find them to be funny (and I love puns). It's things like Lonely Island on the Sydney Opera House art and "He Threw a Car at My Head!" that just make me facepalm. Yeah, it's funny, but I think Blizzard (I can't believe I'm saying this) had the right idea on this. The Druid talent "Blood in the Water" used to be called "Om Nom Nom" in test builds. When it was changed, they said it was because "Om Nom Nom" was a placeholder, and keeping that as the name would be funny for about 10 seconds, then cease to be funny, then just be horrendously lame in a year or two when we get past the point where making those sounds is funny.
I guess there are also just really bizarre choices like Panzer "Schafernator" General, Tea and Crumpets for Everyone, I Can Haz Nukes, and the existence of the My Little Pony achievement that make it seem like the creative team was in its early teens.