JSUE is reworked version of JESawyer tweak mod. It was created by one of original Fallout designer Josh Sawyer but the original version of the mod is gone and people recreate their own as to make improvement out of it (in term of the scripting effectiveness and newer code standard of New Vegas Extended Script modding).
The list of the changes is huge as it overhauls some stuffs within the game. Here is the list of the changes if you are interested to read them. Things that I noticed when I played with it is that you had to make use of Ammo types mechanics, you had to use AP ammos to punch those Super Mutants, Deathclaws or anything that have high DT otherwise you wouldn’t punch their HP much through their thick skin/armor, Hollow Point ammos are ok if you want to save some bullet on lower armored High HP enemies. Carry weight is even more lower than vanilla (though you can change it in .ini file; I don’t recommend to add more than +50 lbs of carry weight to keep it in spirit of the tweak) which forces you to planning ahead during exploration and use those Mojave Mailboxes when you want to transfer some stuff from locations. Survival skills worth the investment in this tweak as chems item is more rare. On my playthrough, I find Hardcore Mode with this tweak really good combination as to make food, chems, drinks and beverage more useful than simply to restore (or buffs) your character stats.
Oh another tip, if you have both Fallout 3 and New Vegas, consider to try Tale of Two Wasteland on your next playthrough, it simply better experience if you want to play Fallout 3 as it use New Vegas engine which more mod supported than 3 version (finding modern mod and bug fixes for 3 is harder than New Vegas based on my last Fallout 3 playthrough).
In my opinion both game are great in their own way and Bethesda did good job saving the IP on Fallout 3 (Bethesda bought Fallout IP when Black Isle/Interplay bankrupt). Without Fallout 3, New Vegas can not exist.