dybuzam - here's some more details of what I thought of the verbal challenges and where I feel they could be improved :
1. The SCs are rather straight up. What I mean is, more often than not, they only test one concept. A typical GMAT SC is not that robotic, it tests 2-3 subtle concepts and it throws answer choices that look correct, but are not. Also, the GMAT sentences tend to be longer. This is because GMAT test creators put in lots of "padding" in sentences to obfuscate the meaning of the sentence. GMAT also tests the overall meaning of the sentence quite frequently. Furthermore, GMAT sentences are out of publications, books etc. The sentences in the challenges felt very "contrived". Its not they are incorrect or are a poor test, its just that they don't "feel" like the real GMAT (I could argue the same about MGMAT's verbal tests).
2. CR - we can debate this one till the cows come home, but after looking at several LSAT and GMAT (and MGMAT, Kaplan
CRs), I felt that the CRs in the challenges were more open to debate - i.e. they were not water tight enough.
3. The order of the questions. This is a minor gripe, however, it may help usability of the verbals. Typically GMATprep throws at least 2-3 CRs , 1 passage (3-4 questions) and 2-3 SCs by the end of the 1st 10 questions. The variety might have something to do with its internal scoring algorithm. The challenges should try to "mimic" this order, at least initially.