I'll always remember the chase sequence in Episode Four fondly because it was the only time ever that my father sat and watched Doctor Who and was mildly interested in it. He even asked me a couple questions about what was going on. Sadly, he has never seen an episode since then, nor has he expressed interest to, but I will cherish those few moments for decades to come.
It's the fact that such a chase could provoke a response out of even the hardened opponent to Doctor Who is a testament to how much better Episode Four is than the previous three installments. Once things shift away from continuity and collar heavy Gallifrey and the story gets to the raw meat of the matter, Arc of Infinity becomes remarkably watchable. Sure, the chase sequence goes on forever, but it's well shot (mostly on the fly), and gloriously shows off Amsterdam (which would have made John Nathan-Turner happy). It's also an ultra rare occasion that sees Doctor Who in a metropolitan setting, something that couldn't be done in the UK without everyone in the street doing double takes once they realize that The Doctor just ran past them.
Best of all is Peter Davison's performance as Omega. Once just a ranting monster, Davison's Omega is a child in a grown man's body, looking on with wonder at his newfound world. The harsh cut from a docile Omega enjoying the street organ show to a frantic Doctor scanning his surroundings to try and track down his prey almost makes one side with Omega. It all goes pear-shaped for Omega soon afterwards, but for a few moments there, you almost hope that maybe Omega can exist in our world and that everything will have a happy ending.
Speaking of happy endings, Tegan rejoins the TARDIS crew at the end of the story. So why isn't The Doctor happy? He seems almost put out by her presence there. For once, Tegan seems happier to be travelling in the TARDIS than The Doctor is to have her there. Ah, well. We've had a bit of a break from bickering in the TARDIS, but it looks like it might be set to return...