Agreed, the best answer for most of these types of discussion is to simply provide users options, which is a rather brilliant, yet anti-climatic solution. However, the interesting discussion comes in the actual possibilities for these options. As has already been mentioned, some might be:
1. Location-specific damage. Head shots are nearly always fatal, while body and leg shots are less so.
2. Realistic damage (and effects - you get shot in a leg, then you run slower).
3. Limited carrying capacity. If you attempt to carry 20 weapons, with 500 rounds each, you'll likely break your spine and won't be able to budge from that spot.
Others might be:
4. Limited running endurance. As you run, you'll start to loose energy until you're forced to rest. Perhaps in MP this statistic can be modified similar to how force points were allocated in JK...you can bump up/down your health, stamina, speed and other interesting stats.
5. Realistic running speed. The days of Cheetah-like speed are over, unless you invoke Force Speed, or take some metabolically enhancing drugs.
6. Believable blood and gore; not gratuitious and absurd, but accurate - showing that violence has consequences, but not in the absurd way that gore is depicted in Quake-ish games - no offense.
Something to think about...