The Quant section of OG, except for the last 60DS questions, is easier than that of the exam. I would suggest you to practice PS from Kaplan
or gmatclub if you want to improve your quant skills. Verbal, however, is very similar to that of the OG. 2 things which might make the exam's verbal section harder is that it seems to be a relatively common thing now for ETS to put back to back RC which might throw off your timing. The second issue is that SC questions seem to be a bit trickier in the sense that you will very likely encounter some of those long and completely underlined SC.