I had actually tried watching The Seeds of Death once before, years ago, and rather bounced off it. I think if you aren't used to Troughton's style, it's difficult to get into him mid-season; I know that when I started listening to the audios last year I found his performance an acquired taste. But once you have been converted it's a different matter.
Also there are two whacking huge problems with The Seeds of Death which may put off a viewer less inclined to be forgiving. One of them can be described before we get to the plot: it is the costumes. The main monsters, the Ice Warriors are fantastic. But the leader of their expedition force, Slaar, is much shorter and has a less ornate costume which unfortunately means he ends up with a close resemblance to Dark Helmet, the character played by Rick Moranis in the Star Wars spoof Spaceballs. And the humans - at least the men on Earth - fare little better, with bizarre trousers which look like they are fitted with incontinence pads.
The second problem is intimately connected with the plot. The future Earth depends on a technology called T-Mat for transportation of pretty much everything. The T-Mat is controlled from the Moon, but its Earth-based secretariat shares a location with other sensitive facilities such as weather control. But there appears to be no serious effort to keep these areas secure, so that a single Ice Warrior is able to throw the Earthside complex into chaos. And when the necessity of launching Earth's one remaining space rocket becomes apparent, they turn to three complete strangers to form the crew (the Doctor, Jamie and Zoe). I think that was the point where my implausibility circuits overloaded on first watching.
But if you can swallow these two points, there is a lot to like about The Seeds of Death. All the actors are great. The Ice Warriors (apart from Slaar, and even he makes up for his comical appearance by carrying off the part very well) are pretty scary, and their take-over of the moonbase is dramatically well executed. The action is kept up frenetically to the point that most will overlook the implausibilities of the plot. On the DVD commentary for the last episode, Wendy Padbury apologises profusely for visibly giggling while struggling to open a door, but in fact it's barely noticeable even if you know what to look for
And there are killer seeds (as in the title) which produce oxygen-destroying fungi. One of them explodes in the Doctor's face, knocking him unconscious for (conveniently) just over an episode. Others produce lots and lots of foam, the like of which had not been seen since Fury from the Deep. Cue lots of Troughton gurning as only he could; I can't think of any other Doctor who actually looked terrified as often as him.
I was fascinated by the list of the main cities served by T-Mat (as already recorded here and here). They are:
New York - BerlinIt is a fascinating insight into where the writers of the 1960s thought the centres of world trade would be in the not-so-far future. Two cities in Canada, two in Scandinavia, two in Germany; but nowhere in Europe further south than Zurich, only one city in Asia and none in Africa. (Including both New York and Washington is excusable, I think; but having nowhere further south or west in the Americas is not.) Anyway, useful material for an article I'm doing for shsilver.
Moscow - Oslo
Toronto - Hamburg
Paris - Ottawa
Zurich - Tokyo
Stockholm - London
Washington - Canberra
All the human characters are white Europeans, but we do at least have two intelligent women (Zoe and Gia Kelly) one of whom is in a leadership position. I'll just also note that Irish actor Harry Towb plays the doomed lunar base commander in the first episode, but does it with an English accent à la David Tennant. (He appears using his native Norn Iron in Terror of the Autons, and with a peculiar Italian accent as the Brigadier's Sicilian uncle in The Ghosts of N-Space.)
In summary, one of the good ones from Troughton's last season.