I really struggled through seasons 3 and 4 but stuck with it for the occasional brilliant songs. I think the problem might have been that they were always on the edge of cancellation, so they packed way too much plot into season 3, then had nothing left in the tank for season four. Because in the first half, NOTHING happened.
New Gregg never worked for me at all, either.
That said, the last couple of episodes were very nice, if predictable. I found the date between Rebecca and Josh in the penultimate one to be really sweet.
There's also a live show on Netflix which is lots of fun, if a bit rushed.