The general audience probably also expects to tune in to an adventure involving the Doctor and his companion each week, yet in the modern era it's become an annual tradition where the Doctor and the companion have a reduced role to just one or two scenes and the episode is mostly carried by guest characters. In fact, one such episode (Blink) has become so popular it often tops lists of the best episodes of the modern era and usually ranks pretty high (usually in the top 10) on the best episodes overall as well. Just saying.
Of course we'll still have alien monsters to fight or befriend as seems appropriate, and the Daleks will still make us wonder if the BBC really is contractually obligated do a Dalek episode per year. But we can also have variety too.
Although I agree the episode could have worked fine without the alien creature, I'm actually okay with it in this case since the alien's death scene where we learn it's just scared and lonely rather than evil and threatening really was a well-done scene.
I've recently rewatched that episode and it is a nice scene. Also there's a nice symbolism. Van Gogh is shunned because of mental health, the creature has been shunned by its own kind due to physical disability.