It doesn't always work; the part with the Doctor trying to prove to the UNIT medical officer, Harry Sullivan (as played by Ian Marter), that he's in perfect health is pretty good, but the scene where he keeps reemerging in different costumes is perilously close to being too cute for its own good -- and Dudley Simpson's "funny" score doesn't help things any. The other issue with this scene is that, while all the other costumes look like unified ensembles, the fourth Doctor's final look doesn't, and so there's a lack of continuity in the thought process here.
But while they're trying to make Tom Baker stand out as a new and different Doctor, the story they've chosen to give him feels like a fairly typical UNIT adventure: something immensely strong and powerful has been stealing various top secret plans and sophisticated scientific equipment, and it's up to UNIT to figure out what's going on. In what's likely a direct contrast to Spearhead from Space, after the initial bits of scatterbrained behavior from the Doctor, he settles down quite quickly into his new persona -- it doesn't take him two episodes to become involved in the main plotline. It's just a pity it's such a standard tale.
I'm probably making things sound worse than they are. Make no mistake; these two episodes are entertaining, and there are some good directorial choices from Christopher Barry. The decision to film everything on video, even the exterior scenes (the first time this has happened on Doctor Who), gives the production a nice consistent look (although the technical reason for this decision will become apparent in episodes three and four). The "robot's-eye" view early in episode one is also a nice touch, while the scene of Jellicoe working on the robot in part two has the (presumably intentional) flavor of Frankenstein working on his creation. And it's always good to see Sarah working as an investigative journalist -- both in her exploration of Think Tank and her brief encounter with the (oddly combative) representative from the Scientific Reform Society, a sort of fascist/technocratic organization. There's a conversation between her and Think Tank director Hilda Winters about her feeling that the robot is alive in some sense -- "I think you must be the sort of girl that gives motor cars pet names" -- that subtly but effectively puts us on Sarah's side and not on Miss Winters, given that the show's main character drives around in a car named Bessie. And finally, the design of the K1 robot is very good indeed, as it towers over everyone around it. Really, it's hard to point at anything that's not at least competently done. An encouraging sign for the two remaining episodes.
But it has to be said: the sight of Tom Baker driving around in Bessie is deeply weird.