Multiplayer is actually possible, and I've done many 4-player co-op games with System Shock 2 in my life. I've completed the game close to ten times with 4 people.
Do a google search for "SS2 multiplayer guide" and check out the first link displayed. I'd link it myself, but apparently GOG has that feature disabled for general users.
Follow the advice there, you should be able to work through it and get it up and running with enough effort. With enough patience it's definitely possible. It is only impossible with particularly problematic router or hardware configurations, and even then I find that it is often actually possible, it merely requires a good VPN or some know-how. Do your research, and you'll get it working.
Oh, by the way -
The most common issue with the desync is a lack of proper port forwarding. Be sure you have the following ports forwarded:
TCP & UDP: 2300-2400
TCP & UDP: 28800-28900
And be sure to set the trigger port to 47624 (both incoming and outgoing (firewall) if it asks).
If you don't know how to do these things, look it up on google - there are many good guides for whatever brand of router you may have.
And one last thing - pardon for the posts, I just keep forgetting to mention things.
Save before every bulkhead and you'll find that multiplayer frustration is kept to a minimum. It really does not take long to get everyone back together once you get all the proper ports forwarded and multi figured out, and reload times take all of half a tick. Most of the infamous "constant" crashing is just on level changes, so quick saves before every bulkhead prevents frustration there.
It's worth it. SS2 is a completely different and awesome experience in co-op, and I hope Night Dive or the community eventually patch the multiplayer to be more stable.
All of this said, I played multiplayer for 4 hours last night with a friend and we did not have a single crash, and I've played this game in the past with 4 people many a time before the compatibility patches with minimal crashing too. It really isn't as notoriously buggy as people make it out to be, at least before Windows 7 came out. 7 did NOT like the engine SS2 runs on. But Night Dive (and the modder who originally modded up the engine with the New Dark patch) fixed that for us.
That ALSO said, I HAVE run into people that get tons of crashes in multiplayer. It just hates some rigs for multi. Here's hoping yours isn't one of them and you can work around it.
Post edited February 16, 2013 by Icefoxen