The first episode of Arc of Infinity is a rare glimpse into what could have been for the Fifth Doctor era - a Doctor/single companion relationship. It's almost refreshing to see both The Doctor and Nyssa getting along, as well as having something to do. The intervening adventures between Arc and Time-Flight before it would give the Big Finish writers considerable fodder for episodes, but it's a shame that this pairing was not given more screen time.
The scenes in the crypt where the two hitchhikers are thwarted first by poor sleep, and then by a giant chicken, are actually quite moody (at least until the chicken turns up), and when Andrew encounters a possessed Colin, it's almost bone chilling. As the explanation for the bizarre appearance of the Ergon (aka "The Chicken") won't be given for a couple more episodes at least, leading off with his unannounced appearance is not the most effective way to build up the image of an effective monster.
There are two things that really bug me about this episode, though. The scenes set on Gallifrey just sort of happen, with no buildup or introduction. We're given a brief pan of the surroundings in the first shot in Amsterdam to show that, yes, Doctor Who is not in a quarry, nor in a sleepy English village, but Gallifrey is not accorded the same treatment. It's almost as if Gallifrey has become as familiar to viewers as the Home Counties have, and why not? The words "Time Lord" and "Gallifrey" have become mentioned in almost every story in the 1980s so that by the time we actually land on Gallifrey, there's no fanfare. We've heard about it all before.
The second thing that irritates me slightly is a line The Doctor speaks after the recall circuit has been operated, automatically sending the TARDIS back to Gallifrey. He says, "Only twice before in our history has the recall device been used". Why is it essential to say that it has happened precisely twice? This line is only useful to two related groups of viewers: the group that vividly remembers watching both The War Games in 1969 and The Deadly Assassin in 1976 (or the repeat of the latter in 1977), or the group of slightly less anal retentive fans who have perhaps only read the novelizations of those two stories. Such a line dangerously flirts with alienating new viewers, especially in light of the lack of solid introduction to The Doctor's home planet. A much less generic line of "It's rare in our history..." would have been just as effective, while still maintaining the severity of the situation. I can only assume that the original line was Ian Levine's inclusion to the proceedings...