If it's so WTF that you can't finish it or fairly analyze it, identifying what's wrong with it and an objective reason for the WTF-ery, than yes, send it back.

Otherwise, write a fair and honest review. If you're feeling kind because it's a newbie, go back over it afterwards and excise any/all snark. You'll never get published by Kirkus that way, but it's better for your conscience :-)