The Invisible Man can be considered a tragedy, but it fits much more snugly into that plot if you put the story in chronological order. So we'll start with the Invisible Man's own story that he tells to Kemp.
The Invisible Man is an unhappy student-teacher who wants to be more than he is. This is a classic beginning for a tragedy: a protagonist who feels unfulfilled because he wants more. But there's one tiny detail that keeps The Invisible Man from being a regular tragedy: we don't really like the protagonist. There's not much to like about the Invisible Man. (Certainly, by the time we hear this story in Chapter 19, the Invisible Man has given us plenty to hate about him – like killing innocent people.)
The Invisible Man has a simple dream: he just wants to invent an invisibility formula. Is that so much to ask? He succeeds in inventing the formula, so it seems like things are going his way. Although, we should note that there are certain issues that prevent this from being a real dream. For one thing, the Invisible Man steals money from his father and his father then commits suicide – not exactly a standard dream stage.
It turns out that being invisible isn't so great. He's super lonely and he almost gets caught several times: on the street, in the department store, in the costume shop. It's all very…frustrating.
It's bad enough when strangers make your life uncomfortable; it's much worse when people you trusted turn against you. Marvel turns against the Invisible Man and steals his money and books. Then Kemp jumps on the bandwagon and reveals all the IM's secrets. Suddenly, the Invisible Man has the whole world fighting against him.
Bottom line: the Invisible Man gets killed. It's not so surprising, since he has the whole world against him. That's not great odds. We could call this a tragic ending, but is it really? After all, the Invisible Man was a dangerous guy by the end of the story. So, this might be a tragedy for him, but it's not a tragedy for the rest of the world. Unless, of course, he had a cure for cancer in his scientific notes and it was lost forever. Then we'd be willing to reconsider.