Good point.
Could you elaborate on why it's so great in multiplayer? Just curious!
Sure. First, you might want to read some of my Wargames League after-action reports on my site. Start with the oldest WGL one and work your way to the latest one (Dark Business).
http://dslyecxi.com/shackstuff.html
Here are a few things WGL 5.1 does differently from other mods:
1. Weapon accuracy is more realistic. You have more sight sway when standing/crouched, the recoil is heavier, and the 'zoom' is lessened.
2. Medics and the damage model are much improved. People can bleed after being hit, they'll get temporary paralysis after being shot, they'll leave blood trails on the ground, they'll black in and out of consciousness when heavily wounded/bleeding, and you can bleed to death. Bandages are introduced - not everyone has them, but they can be used to attempt to stop bleeding. They aren't always successful. One very important thing is that players do not die as rapidly as in OFP vanilla - being shot once doesn't instantly zap you out of existence, unless it's a headshot. This makes gameplay in general MUCH more enjoyable than in normal mods.
3. Rucksacks. This allows for increased inventory - you can have a rucksack that carries extra magazines, grenades, bandages, etc etc, and pull out that extra equipment when you're running low.
4. No death messages, no scoreboard during a mission. This encourages teamwork and good communications. You won't instantly know that you killed an enemy, or that a friend just got shot. You have to pay attention and talk to your teammates to keep track of what's happening.
5. Coordination is improved due to the inclusion of group- and unit-tracking systems. With this, you can have map markers follow the group leader as long as they have a radio with them. If they lose their radio, they'll lose contact with the other groups, and will have to reacquire the radio to get updated map marker positions. This can be used in some pretty creative ways in missions, but I don't have time at the moment to give you examples of how exactly.
6. Better armor model. Tanks are more survivable, infantry AT is less effective, and so on.
7. Better AI. The AI will engage you from a longer range, but is NOT laser-accurate. Firefights last muuuch longer and are far more intense.
...and so on and so forth. Those are the basic points but there is a hell of a lot more to it (like the mortar system, improvements to the helos, etc).