Sure, the CSO looks quite poor, and the science is probably completely inaccurate, but is there any more heroic a scene in Doctor Who than the space walk sequence in Episode Four? The sequence is often cited as a particularly memorable moment on clip shows, and with good cause, as it is just a fun scene - plain and simple. Even Roger Limb, whose music would get worse before it got better during his time on Doctor Who, provides a very strong and jaunty score.
Really, Four To Doomsday is just like the space walk scene in that the story, as a whole, is just plain fun. It's a wonderful space romp that is far too often overlooked, and contains strong pair of performances from Philip Locke as Bigon (who you just want to cheer for because he's so noble and helpful) and, especially, Stratford Johns as Monarch, who sounds so natural and so infuriatingly charming that you almost understand why Adric was so keen to stand by his side as he did his best to rid the people of Earth of "flesh time". Further kudos must also go to Paul Shelley as Persuasion (or "Percy", as The Doctor calls him, which is delightful).
But the highlight of the episode, and possibly the whole story? Look how distinctly bothered Annie Lambert as Enlightenment is when she's watching the Greco-Roman wrestling exhibition taking place in the Recreational Hall. Seeing Lambert squirm in her seat is just about the sexiest moment in 1980s Doctor Who.