Downside is that your framerate was capped to the person with the slowest computer, and there was always that guy with the 486sx25 who got invited to play.
The perpetrator was never caught.
Some configuration, but you don't have to update the port forwarding as often as you would expect.
The reason you can't just play games with your friends anymore is that game companies make way too much money from skins and do not want you to be able to run a version of the server that does not check whether you paid your real money for those skins. Weirdly, despite literally inventing loot boxes, Valve does not suffer from this sometimes. TF2 had a robust custom server community that had dummied out checks so you could wear and use whatever you want. Similar to how Minecraft still allows you to turn off authentication so you can play with friends who have a pirate copy.
By the way, this is why bnetd is illegal to distribute and was ruled such in a court of law: authenticating with battle.net counts as an "effective" copy protection measure under the DMCA, and providing an alternate implementation that skips that therefore counts as "circumvention technology".
It's like in-engine Hamachi. Works really well with P2P games.