The genre of the rejection letter is more formulaic than any kind of pulp fiction.
A: Thanks for sending me this!
B: While it shows promise...
C: ...I just wasn't into it.
D: But keep trying—someone will love you.
Works for job applications and breakups, too. "It's not you, it's me."
When I review for the Journal of Environmental Psychology, the reviewers are asked to give a score to the editor ranging from -3 to +3. If I remember correctly, the scores correspond to something like this:
3: this article adds immensely to the field, and will become a core of the literature.
2: this article is quite strong, and deserves publication with no or few revisions.
1: this article is competently done, and can be published with revisions.
0: this article has significant flaws, but I believe that it can be revised profitably.
-1: this article is unlikely to be successfully revised, but I'm willing to review it again if you think otherwise.
-2: this article is unlikely to be successfully revised, and I'm not interested in seeing it again.
-3: this article is essentially inept and cannot be saved, because the underlying research is so badly flawed it can't tell us anything.
I'd love to see, instead of canned form letters that we have to dig around in like chicken entrails, agents simply send us back a number corresponding to something like the above (for instance, a 2 in fiction might mean "this is a viable project, in a genre that I don't work with"). Any one agent's review can be dismissed, of course, but if a MS gets a whole series of 1's and 2's, then there must be hope. If it gets a string of -2's, then I have to rethink the whole thing.