The Monster of Peladon, from 1974, is probably the least memorable of Sarah Jane's first series with the Third Doctor. The Tardis returns to the scene of an earlier adventure, but this time the politics is really clunky rather than subtle; Sarah tries to teach the Queen about feminism, the miners are revolting (as they were in real life at the time), the Ice Warriors are baddies again, the most interesting character (Chancellor Ortron) is killed off far too early, and the whole thing is (as so often with Pertwee stories) a couple of episodes too long. One for completists really. I recognised Eckersely as Bob Hoskins' sidekick from adult literacy programme On the Move.
The Talons of Weng-Chiang, from 1977, is the climax of the great Holmes/Hinchcliffe era of Doctor Who (also the last directed by the superb David Maloney), and is as good now as I remember it being when I was nine. (I admit I have also seen it a couple of times since, once in the company of a girl from Manila who giggled pleasingly at the line about the Filipino army advancing on Reykjavik.) Thanks to my background reading I was now alert to look out for a particular shot at the start of episode 4 which had escaped my notice previously (on the DVD commentary track, Louise Jameson laughs loudly). There is so much great stuff here: Leela and the Doctor are both alien to Victorian London, so Jago and Litefoot are effectively the viewpoint characters; Deep Roy, later to play hundreds of Oompa-Loompas in Tim Burton's Charlie and the Chocolate Factory, turns in a great Mr Sin. Yes, the ethnic stereotypes are rather regrettable (and quite apart from the Chinese, I would draw the attention of Irish viewers to Chris Gannon's Casey), but the setting and drama are just fantastic.
Jon Pertwee's first season in 1970 was certainly his best, but also in a lot of ways quite unlike any other season before or since. The Ambassadors of Death is Who as James Bond-ish adventure story with lots and lots of shootouts and fighting, and aliens who can kill at a touch. I though Caroline John as Liz Shaw was particularly good here, though she does scream once or twice. Not quite sure what the point of the time experimentation at the beginning was. The plot was exceptionally convoluted in order to cover the seven episodes, and I felt the camera lingered on guest star Ronald Allen for longer than the quality of his acting really deserved (some of the other recurring actors, eg John Abineri and Michael Wisher, were rather better I thought), but altogether it is pretty compelling. It's quite uncomfortable and spiky in places; the congealing of the UNIT "family" in the next season made for a much safer and basically less exciting programme.
So, in summary, one total classic, one interesting (if you can bear to take in all seven episodes) and one for completists only.