All 2002-2005 have same bad window regulator problem with occasional failures, $170 for the replacement part. I replaced one myself in the rear and it was easy. The dealer also updated the driver's window regulator with the newer version, and that has already been replaced under warranty. So maybe the newer ones are not perfect either. I also had some problems with the transfercase control module that seems common in the rearly MBUSA G500's. That was fixed over a year ago with no probs since.
It seems that the problems that gave these models a bad reputation early on have been pretty well sorted. If I was looking right now, I would focus on a lower mileage truck and just use it as a daily driver for a few months to assess for issues prior to modifying it and taking it offroad.
I have put 15K miles on my G500 in the last 18 months and am very happy with the purchase.