Today, just about every rule in the book was broken. In series past, the doctor would say with a grave expression that he was the last of his kind and that he could never return to the time war. We were also told that if he ever crossed his time stream it would be disastrous.
Well we saw him dance all over his time stream today and stop off via the Time War for a loaf of bread on the way home, saving all the other Time Lords in the process. Not destroying Gallifrey was a massive cop-out and totally removes any darkness or emotional weight that the post reboot series had. The Doctor's broody back story was probably the most interesting aspect of the character but now that's effectively gone.
Today's plot even invented a new rule in the form of a Tardis-proof room only for the doctor to find an alternative means of entering in a matter of seconds. If the Doctor isn't limited by anything, how are we supposed to be emotionally invested in the plot?
I'm sure someone will have a lengthy, contrived explanation as to why everything that happened today was possible but it doesn't matter to me as it shouldn't have been. Once the rules and mechanics of a fictional universe have been set, they should be stuck to!
Also, the Tom Baker cameo made no sense...at all.
All that said, this episode did manage to raise a smile from me so I suppose it's been successful on an entertainment level. I just wish that the show would treat its own story line with a bit more reverence.