I just took a practice GRE CAT from Manhattan GRE (yes Manhattan GMAT now does GRE prep!). It has been six years since I last took the exam and after all this GMAT frustration I just wanted to see how the tests compare to each other.
The GRE math section is way easier!!! Obviously it does not have data sufficiency, instead it has a data comparison section where you are given a question and then two separate values in two columns. You must determine if Column A or B is greater, equal, or you cannot determine with the amount of information given. I did best in this section; I got a 550! I think that score may be higher than when I took the real thing. There is also a section where you have to interpret graph information. I didn't remember that section so it was a surprise when it popped up.
The verbal section is very different than the GMAT. Our buddy reading comprehension is there but the other question types are completely different: sentence completion, antonyms, and analogies. I did worse on this section than I did on the real thing: 390, ouch! There were lots of words I probably knew at one time but I don't know them any more and it made it impossible to get any of those questions correct.
Taking this GRE CAT has given me a better appreciation as to why b-schools want a GMAT score and not a GRE score. The GMAT is a much more difficult test. I have a better understanding as to why the AdCom uses it as an indicator for how you will handle the rigorous MBA curriculum. This just means I have to study harder!