Does this work for a thesis? "Many have criticized Hemingway; however his use of symbolism is effective in getting his point across."
I would like to add an item that I hope will complement mshurn's excellent comments. If you choose to include a reference in your thesis statement to the "many [who] have criticized Hemingway," you will want to be able to address that item in your essay. As a rule, you should not bring up something in the thesis statement that you don't demonstrate or present.
Early in your essay, perhaps even in the second paragraph, you could include a summary of two or more critical statements that reflect the view of the "many" whom you have in mind. If you don't have the examples to present, however, I would recommend that you drop this part of the thesis statement altogether.
While many have criticized Hemingway for being overly symbolic, he effectively employs symbolism to make concise philosophical statements about the world as he sees it.
I think this thesis can be supported with evidence from many different works by Hemingway, including short stories as well as novels. My only suggestions would be these.
1. Are you writing about one specific piece of Hemingway literature? If so, you should include its title in your thesis.
2. I would suggest polishing the word choice in your thesis a bit. Instead of "criticized Hemingway," consider "criticized Hemingway's work" or "criticized Hemingway's writing style."
3. Finally, "getting his point across" doesn't use the vocabulary of literature. Try this instead: "developing his theme."
Good luck! Hemingway's work will give you much to work with in writing your paper.
Oops, one more thing! In your thesis statement as you have written it, you do need a comma after the word "however."