thb
As it is hard to find real challenges in the usual GMAT learning materials, this is exceptionally valuable.
On what basis did you assign the GMAT score to the questions? I guess, it´s mostly by experience and a bit by rule of thumb!?
Anyway, I hope you can keep up your work.

The score was "assigned" by a mutual consensus between several experts who worked on the test, so it is not anything scientific.
GMAT has the privilege of knowing the exact difficulty of every question by trial and error (experimental questions) - we do not, so we had to rely on our experience. As you can see, however, several questions are above/below the level they are posted and that revision is coming.
This test is a community project, so if you feel some of the questions are too easy or too hard - please post that in each of the questions - we'll take it into consideration for the next revision and yes, feel free to criticize the heck out of it