For my money this was an utterly stunning episode.
First, a word about the monster; honestly, the monster is no less silly than just about anything in Nu Who. It is the nature of Nu Who at this point and a part of the show. Also, it deserves some credit for being worked well into the physical comedy of Matt Smith with the mirror contraption. Overall, the monster could have been done better, but it was perfectly acceptable for its purpose in the story.
As far as I am concerned this is the finest character piece in all of Nu Who. When I realized where the episode was going, I was very unsure - taking on Vincent Van Gogh and in a time period so close to his historical suicide is an incredibly touchy idea when one stops to consider it. It easily could have gone off the rails into absurdity, morbidity, or disrespect. It has become clear to me though, that there is a certain theme running through all of Nu Who even early on:
That theme is taking historical figures and humanizing them. When Shakespeare appeared, I appreciated the subversion of focusing on the historical truth that he was in his own time a tacky and lowbrow entertainer who had a genius for words that flew over the heads of his contemporaries. Something that bothers me is how figures in history are enshrined in marble and treated with, in my view, the wrong kind of gravitas. The real Shakespeare, in spirit, is more there in Nu Who's portrayal of a rowdy cursing man than in stone busts in museums.
But the way Van Gogh is treated is divine. While it is true that the script is at moments thick and a bit sappy, if ever there was a misunderstood artist who deserved that, it is Vincent Van Gogh. For people who are not aware of the fine details of Van Gogh's death, his suicide was not quite the typical scenario one might imagine. Van Gogh shot himself in the chest with a pistol in a field, but he failed to die at that moment; he believed the shot was not fatal and returned to town. Unfortunately, his condition grew worse and he died two days later.
The thing is, to me this does not bespeak a man who utterly failed to fight his demons. Vincent tried to turn back on his decision; it is a tragedy that the medical care available at the time was unable to save his life.
At the time of Van Gogh's attempted suicide/misadventure, his work was just beginning to proliferate and only a couple of years later, would have the chance to be exposed to the word at large. Bill Nighy's character was not overstating the impact of Van Gogh on art. Even though it's said that artists are never appreciated in their time, it's utterly stunning to realize how much Vincent changed the world just after he died. What makes the tragedy bite is that it wasn't a distant reconsideration of an artist decades or a century later but literally just after he was gone.
Above all, this episode treated Van Gogh as a real person, with reverence not for him being an icon or an important figure, but for being more human - in all of his troubles - than most human beings will ever be. The ending and bringing Van Gogh to the future to see the result of his works is kept from being camp and tasteless by the Doctor's superb explanation of the truth of life. That the good and bad will always be mixed together, and this is a truth to be faced head on rather than looking away out of politeness, embarrassment, or denial. (Did I mention that in this episode, Matt Smith has finished utterly and completely selling his Doctor? Signed, sealed, and delivered. "Overconfidence, this bag, and a screwdriver.".)
The way Van Gogh's view of the world is explained in this story is also one of the finest examinations of the nature and process of art in the history of popular entertainment. In a sense, I truly believe this one story does more to explain the nature of Vincent Van Gogh than any university course in art ever has.
That's just some of it; there are dozens of brilliant things I could point out that all went into the show. It's the natural result of when an idea, a script, and a cast come together flawlessly.
So yeah, it's kind of like that. This wasn't an outstanding Doctor Who episode; it was one of the best hours of television I've ever seen.