One of the great Robert Holmes' most overlooked stories is this witty gem that makes lots of sly digs at the Inland Revenue, grey-faced civil servants, and beauracracy in general. It's one of Tom's most entertaining stories, and while the actual plot is pretty straightforward (the Doctor bands together with some rebels to defeat an opressive regime) the way the story is told is really enjoyable and the story is full of surprises, great characters and wonderful dialogue. This story marks the mid-point of Tom's reign as the Doctor and it's about here that he starts to dominate the proceedings to a greater degree, making sure the focus is more clearly on him, and beginning to have a little more fun in the role, though not yet going as over the top as he would do a bit later on. The scene where he meets with the Gatherer is one of my all time favourite scenes with lots of witty banter and the Doctor managing to insult the Gatherer without him even realising it - "Humbug?" he says, offering him a sweet but clearly showing what he thinks of the Gatherer's policies. The Collector is another superb character, played like the ultimate grey-faced civil servant, and the actor's diminutive stature, whiny voice and motorized wheelchair make him a very memorable villain.
Louise Jameson also gives, in my opinion, her best performance as Leela, she is superb in the scene where she stands up to the rebels, and K9 also gets a good outing here.
Some people have criticised the rather minimalist set design, but I think the blank corridors and under-dressed sets actually work to the story's advantage. The location filming of the long tunnels, corridors and the rooftop scenes also add much to the story's impact.
The Sun Makers is a wonderful story, that repays repeat viewings and is one of the highlights of Tom's era.