If you use the search button you should get listed what you want.
using google there is plenty information too.
there haven issues with the gen4 9mm.. mostly with the g19...and the latest gen3 some seems to have erratic ejections issues as well as with the gen4s..
the gen4 has interchanble interchangeable back straps but that depend of the size of your hands.. the trigger on gen4 is harded than gen3.. the grip texture is different too. the mag release is extended, so for people with small hands is easier to release the mag..
for ME, I think the recoil is little lighter in the gen4, due the double recoil spring..