The final Tom Baker story is now available on DVD, and it was worth the wait. Those who've only experienced the Zygons from the 50th anniversary special should check this out to see where they came from -- it's a great story that rarely disappoints.
They've done the usual excellent job at restoring this -- I can't help but notice that one of the weaker shots, the one of the Loch Ness Monster in London, has been stabilized so that it looks a lot better.
All this and bonus features too! The documentary is interesting, plus there's a nice vintage piece about oil rigs hosted by Elisabeth Sladen. And the fabled "lost" opening of Episode 1 has been discovered and lovingly restored, allowing us to see this as it was originally intended to go out.
tl;dr: This is an excellent example of 70s Doctor Who, with great special features.