The Mysterious Planet was Robert Holmes' swan-song, from 1986. He wrote some of the best stories of the original Doctor Who run; this is not one of them. It's the first segment of the infamous Trial of a Time Lord season, with the action of the main narrative (the Doctor and Peri land on a mysterious planet and must prevent the local bad guys from taking over the universe; also confusingly it may or may not be a far future Earth) frequently interrupted by flashforwards to a courtroom where the Doctor is on trial, the main story being presented as evidence for the prosecution.
The trial sub-plot simply does not work. There appears to be no due procedure that makes any sense; the evidence presented by the Valeyard (at least as far as this story goes) doesn't do much to prove the case (as even the Inquisitor admits). If you simply tune out these deeply embarrassing bits, you are left with a fairly standard story: a couple of decent performances from guest actors, and a couple of very cardboard-looking robots.
Attack of the Graske is an interactive game on the BBC website featuring David Tennant as the Tenth Doctor, inviting the young viewer to help him prevent the eponymous Graske from ruining a family Christmas (it went on-line immediately after The Christmas Invasion was shown). The logic puzzles are not terribly taxing but Tennant is at his most charming and chummy, and there is a nicely done (if slightly pointless) scene in Victorian England.