Percentage based XP loss modified by player levels.
Low levels lose little experience (less than killing a rad scropion might net them) while mid-levels end up set back a bit. Dying at level 21 weakens your SPECIAL's by on or two points instead lasting 15-20 minutes or so. Conditional: You can not lose levels in this way, your experience can not be decreased lower than the minimum required for your current level - important to prevent greifing so one dude doesn't just set up on a nother dude and set him back days worth of XP in an hour.
The result - less time felt wasted on nonsensical busy work quests, click this now click that, click this now click that. The game shouldbe fun not tedious out the arse which it can do masterfully thanks to an interface system over a decade old. Low levels die well that's life at low levels, oh wel you lost a couple of XP, too bad so sad... go kill a rad scropion or a molerat and get it back again. Mid level died? Harsh dude, I feel for you, gonna need to find a few random encounters, brush yourself off and pick yourself back up. Max level and died? Well you keep your experience but the trauma's left you a bit fatigued you're going to have to be pretty careful until your head clears up and your body stops aching, old timer.
The point is death needs to set you back a bit so you have cause and want to avoid it, but it shouldn't be a PITA that puts you through dated interface manipulation and click fests. I'm not a fan of time sinks in games, they already are time sinks. This is technically a time sink but its not obvious "Do this stupid nonsense thirty times and I'll let you go," it's an "Aw crap, I died and now I gotta go kill somethings to level up again, oh well at least I like shooting stuff!"
I'd also like either more hotels (infinite hotel size please, don't give me that immersion crap as a reason it can't be done - there's three hundred vault dwellers running around start there if you're going to fix immerison) or, yes, respawn near closest city/settlement/town/whatever-you'd-call-some-of-the-filthy-hovels-that-populations-gather-into-in-Fallout. Nothing is worse as a character starting out then getting some momentum then dying by freak chance and getting booted half a state away from your tent/stash of crap in a town.