I only play on LAN, so I can even set up as much instances as I like with a single CD-key \o/
(still, I bought the game several times, so I probably have a couple valid CD-keys lying somewhere…)

Here Iʼve only played it on Linux for years ;)
But LAN play between Linux and Windows clients worked well last time I gave it a try, as long as everyone is on the same version (1.13d in my case).

The only thing Iʼm missing by not playing on Battle.net are the ladder-only runic words, but I think I remember a mod adding these in the solo and LAN modes.

I started playing solo because all my friends moved on like 15 years ago, and I got back into it a couple of years ago. Runewords are nice but not needed unless you're speed running.

The game STILL feels more balanced than Diablo 3, but it might be nostalgia speaking.

Oh, I actually do not need them, but I still want them ;P

Fair point :)