Someone could do this when Series 3 has passed but I can't be bothered to wait that long so I'll include the Christmas Special as well. Rules are simple:
+3 to your favourite episode(s)
-3 to your least favourite episode(s)
you can play once every half an hour. So that gives you maximum play!
I'll start by:

The Runaway Bride 9 (-1)
Smith & Jones 12 (+2)
The Shakespeare Code 9 (-1)
Gridlock 10 (-1)(+1)

Isn't it a bit...early to do this?

very early!