Perhaps we're all expecting every episode of Dr Who to be a minor masterpiece? This is early evening family entertainment we're talking about, not the latest Austen adaptation, after all.
I watched the first repeat of Planet of the Dead with a certain amount of trepidation, having only caught the last 5 minutes on Saturday, and I was pleasantly surprised. I thought it was an enjoyable bit of fluff which hung together reasonably well - not the best thing since the new series started, but not the worst by a long way ("Fear Her", "Idiot's Lantern" being two horrors, IMO).
If I'm going to sound picky, I would point out that the bus was of a type rarely, if ever, used in London, and that its registration changed on at least one occasion, but that would make me sound like some kind of rabid bus-spotter, so I won't. Apart from that, I didn't spot too many continuity errors or gaping plot holes.
To me, the main problem with these new shows has been, and remains, the 45 minutes per story format (OK, this was an hour-ish, but my point still stands!). These days, any time spent on atmosphere is time lost for action/dialogue, and vice versa, which always leaves me wanting more. Fair's fair, some of the old 6 episode stories left me wanting less, but I still think that the old 4 episode stories worked best. The same is true of the new show - the 2-parters seem to linger longer in the memory, for some reason.