I enjoyed it but didn't love it.
Having the 4th & 8th Doctor's together was a fun idea but a bit of a lost opportunity really - neither seemed to have an opinion on the other and once Leela & Charlie were gone their interaction was pretty dull. I know this pairing was mainly for logistical reasons but more could have been done with it.
The 7th Doctor seemed wasted - he hardly made any contribution and none of the other Doctors really reacted to him - They could have played up the contrast between him and 6 or 8. Though saying that the scene with him and Peri was nice.
Loved the 5th Doctor & Neela on Earth sequences were great, very creepy though yes Nyssa not really reacting to the Master felt awkward. I can understand why Briggs went with Nyssa in that Sarah Sutton has always supported Big Finish but using Tegan would have avoided that issue and livened things up a bit.
In general the companions could have got more of a look in and would have made the whole thing more interesting.
I have no issues with who voiced 1, 2 & 3 but the added treatment to the voices did make it hard to figure out who was saying what.
To be honest from the extras Briggs heart didn't sound in it so no real surprise it didn't amaze. He seemed to have been the one to write it because he is head writer not because he really cared and although I don't think he's a bad writer I don't think he's really good enough, certainly not creative enough, to be the one to write all of their big stories - I wonder what a Dorney, Morris or Platt would have made of it.