What are some of the novel's artistic strenghts and weaknesses?
It is difficult to answer this question as currently phrased. It might be better instead to compare the novel specifically to other forms of artistic expression.
For example, let's compare the novel to the short story. In this case, the novel has several advantages or strengths. The novel, unlike the short story, can relate a large narrative that takes place over many years, or many locations, or involving many characters. Novels can also be told from several different perspectives or points of view, whereas short stories are usually told from one. The novel's great strength is its ability to create a world the reader can get lost in. Its limitation or weakness is that, unlike the short story, it is usually not read in a single sitting, and thus requires readers to put effort into getting back into the story after they've left it for a while. Also, in general the novel is thought of as a messy, inherently imperfect artistic medium. Where critics talk of certain short stories or poems as perfect, novels are almost never thought of this way. One could regard this imperfectability as both a strength and a weakness.
Compared to visual forms like theater or cinema, the novel's great strength is its ability to enter the thoughts and inner lives of its characters. Plays can only show characters speaking and acting. And while movies occasionally feature a character's thoughts through the technique of voiceover, this is not the same as being able to peer directly into the mind of a character. Unlike theater and cinema, however, novels are inherently abstract in that they do not directly stimulate the senses. There is no sound or smell, and not much sight: only black markings on a white page. Novels therefore require more work on the part of the audience. And one could call this both a strength and a weakness as well.