I'm a volunteer reader for a literary journal, so I read and evaluate a ton of stories. (Very few are "terrible," but terrible usually shows up in the first sentences.) Of course, the purpose of the story and the needs of the reader/publication both come into play, but I can come up with a few things that make a story less than great (for me). (I'm guilty of this stuff myself, and have to fix it in editing.)
An excess of stuff that doesn't go anywhere. Many early drafts include a lot of "throat clearing." We see the characters meet and exchange pleasantries and talk about Aunt Mary's goiter for a page and a half until they finally say the thing the reader needs to hear. We don't need to read the entire conversation; just give us the important bits. We don't need to see the character wake up and get dressed; just get him out the door. We don't need detail about every knick knack in the room; just set the scene and get the characters doing something. <PERSON> said, "Try to leave out the part that readers tend to skip."
A lack of action. 873
I don't mean car chases, but just human action. What is the character doing as she talks? Making coffee? Changing a car's oil? Fidgeting? Little actions break up the dialog and, when done well, show the character's state of mind. "<PERSON>'s hands shook so much that he dropped the spoon." That reads better than "<PERSON> was nervous." and much better than "'I understand,' <PERSON> said nervously."
Keeping secrets from the reader. This irks me so much. All the characters know what's going on, but the author is keeping it from the reader in order to spring it on them at the end. That comes across as manipulative. If your story needs a big reveal, then make the reveal to one of the characters, not to the reader.
My advice to avoid this stuff is to (1) get yourself some good readers, (2) do enough revision, and (3) read a lot. A LOT. Pay attention to how your favorite authors write. 627