Season three was mostly very poor, its going the way of most comedies, it started off as groups of actual people who had several small quirks in their personality, but were funny in semi normal stories. Series 3 in particular they ran out of idea's and then they start to go bigger and better, or so they think.
Phil went from slightly idiotic and loads of other things to completely idiotic and everything they tried to do funny had to be him being an idiot, Gloria became all about bad english, etc. Take one part of a character and focus entirely on that, and you get a lot of rubbish.
Friends syndrome, Joey started off normal but a bit dumb and the last half of the show he was just stupid and nothing else. Pheobe started off a bit quirky, last half of the show she was nothing but quirky. Monica was normal but a little controlling, then became only controlling.
They've reigned that in, a bit at least, its been significantly better so far this series, hope it holds out.