This is such a fun introduction to the Fifth Doctor. We get some great nods to previous Doctors with this Doctor suffering very badly from post-regeneration trauma (most notably the Second Doctor's 'When I say run, run' and the way the First Doctor would clutch his lapels and say 'Hmm...').

The space-time trap of Castrovalva that the Master and Adric create where whatever direction in the castle you go you end up back at the same square is very clever too, and quite a unique concept. It feels different to other Doctor Who stories past and present. There's a lot of time spent in the TARDIS before we even reach Castrovalva though, and it does feel like they could have either tightened that up a bit, or shown us more of the rooms inside the TARDIS.

The Zero Room is very cool, and it's a shame we have never seen it since, but the TARDIS is limitless and they could really have gone to ball with spending more time inside of it. How about a TARDIS zoo, for instance? Or a museum of all the items the Doctor has acquired on his travels?