I... liked it. I didn't think it was perfect. For example, the finale of the second season was better, and so was the finale of season 2 of Torchwood.
They copped out/cheated (delete as you prefer) on some of the stuff they set up in the penultimate episode, and the victory seemed a little too easy and hurried, despite the extended running time. But the end was very tragic and fantastically handled.
One of the things the end made me realise was that I'd actually grown to like Donna over the series, which I hadn't expected to. As she mellowed, she became much more interesting, and she developed a good dynamic with the Doctor.
I still wish they'd had the same balls Torchwood did for the season end, but then Torchwood is for an older audience.
I hope David Tennant stays on for series 5, because he really has been the best Doctor.