Too much alcochol here, but I'll reply anyway
Of course MP takes a lot, but it gives a lot in replayability. SP is the core...
I disagree about the old games, though. They werent much more professional than any of us. Its just the immersive factor playing you. Try running Quake 2 or Unreal, or Doom, and you'll notice you're used to good graphics now, and the old games just look horrible.
The imagination was a greater factor then, because of the graphics...

As for Killing Floor, I commented it to point out the weak design in MP gaming. It would have been one of the greatest in my list if I could choose my next attributes and skills...They just didnt think thats needed. Same with their next version, Killing Floor 2. Its currently in active dev, but still no choice. You get some perks to pickup, but thats it... No real game-play changing choice...
When we talk about fun in old games, this is what Killing Floor particularly lacks... choice... Havent you played Diablo 2?
And dont say they didnt had their second chance with Killing Floor 2 Its (not a mod) stand alone, and they could have taken it a little further...

No, I currently dont have any MP projects published. The Dreamlord is my first finished (solely) project. It is extremely hard to build a full-scale 3D game alone. I can see the benefit of Android and 2D block-busters...

My next project (probably still solely developed) will be entirely MP concentrated with the SP integrated in the beginning as a tutorial and introduction, like in D&D Online. The core of this game is the MP Tutorial (actually the tutorial follows my development), so its a working example in some way...

If anyone has any questions/requests for features about the tutorial, feel free to ask or contact me in a PM. It is on pause, but it will definitely continue some day, refreshed!

I really want to thank you all for commenting. I feel like I've really made even a little difference in somebody's life.
I hope you master the MP part and I hope we bring this community back up, into the top 10 game engines...