I took both 3 weeks ago now. The main difference is the USMLE question stems are KILLER in comparison. As in it took a lot more brain power to sort through the stem and pull out the info....especially when you were hours deep in the exam. I feel like a lot of the time I would read a question and by the time i finished the paragraph I was like "wait what." The USMLE ck was undoubtedly more difficult than COMLEX 2.
COMLEX question stems were a lot simpler, had a lot of information you could essentially skip over, and had some keywords, vs virtually none on USMLE.
USMLE=rash on the lower extremities
COMLEX=palpable purpura.
COMLEX DID however have straight up out of left field questions that were 100% bull$hit. I had MULTIPLE questions like this:
A patient in your office needs a ride to another physicians office. Who should set up the ride?
A. The nursing supervisor
B. The patients nurse
C. The receptionist
D. The social worker
E. Somatic dysfunction
Like wow, 4 of those are pretty plausible.
I think the ethics questions on comlex were actually harder than USMLE. The USMLE questions were straight up UW style, easy as hell. The COMLEX (in typical fashion) had multiple plausible answers.
Hope this helps, let me know if you have any more specific questions.