If you want a combat challange, just go nuts in a faction base with less than optimal equipment.
Try taking down every BoS member at their base with no sneaking or armour.
I agree about the NCR and Caesar with the assassination squads.... but this last one is also a little anti-RP if you don't want to hurt that faction. I've done it for the challenge, but it would be more fun if it fit into the story a bit better.
Maybe the unrealistic respawns would make more sense if it was the Fiends --or something like a certain new and devastating NV SuperPsycho drug that kept turning regular wastelanders into NEW crazed fiends. ...and they were a lot more numerous and popped up anywhere, and, let's see, how about a quest to find and destroy the cooking site of the nasty SuperPsycho/Meth/PCP. First you have to clear out the horde of foamy-mouthed guards, then you have to rig it to blow like Megaton, but you have to set a timer and
rrruuuunnnn instead of detonating from a safe distance!
BA-BOOOOOOMMMMM!!!! (*the Courier is slammed to the ground even at a half mile distance from the blast.*)(*rain of debris for several seconds*) (the firey glow of the decimated buildings fades slowly. Black smoke towers into the desert sky.)
Woo!
Of course, notes found on guards and computers at the site tell you of a connection to a conspiracy in one or two of the other factions, sickening greed and corruption and, let's say, traced its roots all the way back to the severe and well known mental decline of a pre-war captain of industry.
... and the destruction of the cooking site would still leave large quantities of the nasty chem out in the hands of unsuspecting wasters...
*ahem* :whistling:
At any rate, the FWE mod for FO3 included a chunk of code that tweaked the enemy AI's pretty nicely so they wouldn't just rush the Wanderer. If their health got a little low, they'd seek cover and fire from it when you poked your head out. It got to be really tricky if they had a good gun and the terrain made it hard to flank them.