Well, the real question to the OP is... why has he/she watched Doctor Who
Concur mostly with what's been said.
Season 1 has a very few good moments
Season 2 is an improvement, but not as much as I'd hoped.
Season 3... Season 3... Season 3 is probably some of THE best televised SF EVER. Not for the faint hearted, though.
Season 4 is a good five part story spread over ten episodes.