Series 3 is mediocre at times for sure, and that Dalek two-parter makes me want to claw out not only my eyes but the eyes of everyone who has ever seen it. However, once you reach "Human Nature," it picks up real good. I'd say the highs it reaches are higher than Series 1, so it all evens out for me.
I'm curious to see how this Series turns out. I enjoyed the first episode in a vague, "Yeah, there's the Doctor" kind of way, but I did notice that all the good parts are the ones that have nothing to do with the immediate plot (The Doctor and Donna mouthing things through the window, Donna's conversation with her Gramps, or the Doctor/Donna/Rose sequence at the end). It's like Davies has lost interest in the adventure aspects of the show and is only really engaged with the soap opera/interpersonal relationship stuff. I love that stuff, too, but it feels like the balance is slipping, and I wouldn't mind seeing a little more attention paid to the standalone stories themselves. I mean, the Adipose were great little monsters with lots of potential -- they come out of the fat in your body, and they look really cute? Awesome! -- but they seemed a little unexplored. Aside from the one scene where that woman is entirely converted to Adiposes, there weren't that many interesting moments with them, or for that matter, the main plot itself.