If you aren't enjoying yourself when you log in, take a break. I play every single night but I enjoy every second of it. If it's not something I enjoy, I just don't do it. If there was nothing in the game I enjoyed, I would stop playing.

I second the idea of trying something different if you don't want to take a break. Are there parts of the game you haven't tackled yet? Try them out. Ignore your dailies for a day. They'll still be there if you want to do them later or another day. If there isn't anything new you want to try, then don't force yourself to play. You'll just burn out.