Well, I just watched S2 E9, and I enjoyed it. Not my favorite episode of the season, but still fun to watch. I took it as a tongue in cheek thing. Music was an interesting way to try something different and get to know the characters more. I agree the premise was kind of weak with the space rift or whatever causing the singing.....but, I went into the episode knowing that I had to engage in a little whimsy to enjoy myself. If you are a hard core Star Trek fan that loves the lore and canon, then this might not be the episode for you. If you enjoy watching the cast and characters having fun while performing, then you will get a kick out of it.
Edit: One of the strengths of SNW is that it does not take itself too seriously, and this episode is no exception. For example, the short scene with the Klingons singing and dancing on their bridge while the crew of the Enterprise watched on screen was pure gold.