You get used to it quickly, but it is odd. Putting an explicit "Join" button with some relevant icon next to the channel name would be much more intuitive. It would also clarify, for example, how you leave the channel. Once you're in one, a separate "Leave" button appears at a totally different location in the footer of the UI, but I can't honestly be sure whether or not clicking the channel name would also do the job of backing you out.

I think the discomfort in this case comes from the semantics of clicking an item in a list. Every desktop interface for the last 25 years has taught us that clicking a list-item means "select". This works for text-channels, and I can kind of see how you might stretch that definition to joining a voice channel - though that's more of a "significant action", which traditionally warrants an actual button - but it makes absolutely no sense for leaving a voice channel.