(I suppose I should have been putting SPOILER warnings on these posts - just in case someone hasn't seen everything and they want to. So - THIS POST CONTAINS SPOILERS FOR SERIES 4!!)
Aside from it featuring my favorite New Who companion, none of the episodes in this season are what I would consider "turkeys." Up until this point, all seasons of New Who had at least one episode that just didn't live up to the show's potential, but all of the stories in Series 4 are fantastic and wonderful and I can find very little to complain about them (probably the one I like the least is "Planet of the Ood," but that is nowhere near the worst of anything Doctor Who has produced).
Again, DONNA NOBLE > THE WHOLE WORLD
Oh - and Series 4 gave us this extremely useful gem, which I shall now use to sound the alert for Series 4 Finale spoilers:
And I love the season finale where all the Doctor's former companions come together to pilot the TARDIS and tow the Earth back home. The music there is gorgeous (MURRAY GOLD FOR PRESIDENT OF THE UNIVERSE!) and it's great to see everyone so happy and joyful and everything's so ~*pretty*~