I'm mainly familiar with Geoffrey Beevers through Big Finish, though I've liked what I've heard so far. Not sure if Anthony Ainley makes his debut as the Master here or in the next one.

A woman named Kassia is marrying someone named Tremas - the name of her husband is not particularly subtle. (Though the fact that anything evil that lands on Traken becomes a statue means it's probably not as straightforward as "the Master is in disguise" - maybe he hypnotized Tremas, singling him out because of his name)

Finished episode 1 - Tremas is also played by Anthony Ainley, while the Melkur is played by Geoffrey Beevers.

Mermaid man - evil

Nyssa's stepmother is so obsessed with the Melkur statue that she seems jealous that Nyssa gets to look after. (And the Melkur is definitely the Master - I immediately recognized his voice)

The Master's mere presence on the planet causes the perfect harmony of Traken to break up.

There's a lot of technobabble being thrown around in this episode.

finished episode 3. The shot of the Melkur on the throne is funny to me and I'm not sure why.

I realize they don't have much say in the matter, but the Consuls of Traken seem way to quick to serve the Melkur/the Master despite having objective proof that he's evil.

It seems like a shame that Geoffrey Beevers' Master doesn't really interact with the Doctor directly until near the end of the last episode of the serial.

Finished. Bit of a dark last-second twist, with the Master possessing Nyssa's father and she seemingly doesn't know about it. I wonder how she winds up on the TARDIS, seeing as she wasn't on there at the end of the episode and the Doctor presumably left.

Adric was better than I expected for his first (and only?) outing as the sole companion, though maybe he gets more insufferable in later episodes. (So far, I think his roughest outing was State of Decay)