In a word, "horrendous."
This show barely gets the needle to the level of "amusing" at times, but then settles back down to "unwatchable" at the 20 minute mark. I think one or two scenes I almost -- not quite -- cracked a smile. Their band's "one fan" in the show ran the two main guys off of the screen in level of humor. Maybe HBO should spin-off a show about the stalker fan.
On IMDB, there was some obvious comparison to Tenacious D. The difference is that Tenacious D taps into the rock-angst-hipster-humor of 1970s/80s American adolesence. They connect to us because we all remember loving Ozzy or AC/DC or whatever in 1979. The Conchords don't have that, and the schtick not funny as a result.
I bet most people like this only because of the network this is on. HBO, or HBO fans, have convinced people that anything on their network is good. If this was on NBC or Fox, it would be off the air before the first commercial break. It's about on the level of "Good Morning Miami", though somehow that show made it two seasons.
Speaking of comedy and NZ, I can't wait to see Black Sheep. The trailer for that cracks me up an order of magnitude more than the 20 minutes of Conchords I was able to bear.
Here's the Black Sheep trailer for your true comedy enjoyment: