I've owned the XLS version of the Gen 3 & 4. Besides general design improvements that each Gen has had over the previous Gen, (the Explorer has come a long way) weird door handles on the Gen 4 excluded, The Advancetrac, and Roll Stability Control are near the top of the list. The little message center (including Tire Pressure Monitoring) is definitely a plus, but they did take away 2 gauges. They gave us back a radiator cap on the Gen 4.......still no tranny dipstick. I'm sure there is more, but this was just what I could quickly think of. I was in Oswego yesterday.