I was slightly miffed about the "dude" bit, but I coped, what bugs me in a time travel program is paradoxes, there are many in that episode, but I'll just give you two from the last 30 seconds.
1. Getting to Skaro to potentially killed Davros again: erm, his T.A.R.D.I.S. was just blown up.
2: Killing Davros with a Dalek weapon: hello.. WHAT weapon when Davros is dead?