Anything that doesn't use a gun would be a nice change of pace.

"Experience/level system?"

I like this. I enjoy class-based stuff with leveling of some kind that confers some sort of benefits.

Does anyone remember the The Legend of Zelda: Four swords Multiplayer (on Gamecube)...If this sorts of multiplayer would be available on huge 64-players maps....

More games like SMNC would be awesome :3

Hmm, maybe a contra ( http://www.youtube.com/watch?v=YBMQhKK3Ctk ) styled 2D Side scroller game, with cooperative mode ( 2-4 player )

Level system - good and popular. Realism - very good, but not popular. Really fast paced - not good but popular.
If u use Source engine I think u can create something like multiplayer game based on the story. Like Left 4 Dead (Zombie - popular, but (in my opinion) already sucks). Create something like history mode for 1-12 players (min). Also challenges, survival modes and nice maps based on physics. And level system. But it's only my opinion.

I haven't seen source engine being used for Fighting games. Is this possible? I know it's very out there.

And what about a RPG game?
The Source Engine is very bad for big open worlds. So, what would be the best way to make a RPG, in your opinion?

• The mod called "Kingdom Collide" did a very good medival game. http://kingdomscollide.com/kc/
  (To lazy for clicky's)

The World needs a proper Tank Game.

I would sell my soul to the devil for a really good and half way realistic tank game where at least 2 people are needed to steer one Tank - Gunner and Driver, optional Commander to keep overwatch.

MP Maps should provide a game of at least 10 vs 10, one tank pack against the other with 1 General who can give orders and has limited airstrike capability.

Tanks should be able to shoot SABOT, HEAT and also should have Smoke to pop.
Nightvision should be available.
Hitting the Tank in specific spots should result in broken Chains, a shot into the ammo chamber should not kill the Tank if the commander ejects the ammo quick enough - this is actually realistic. But of course, ammo is gone, but the Tank is forced to retreat and get repairs and restock from nearby Engineers which are controlled by players.

There should be also one spot for one squad by 4 players providing a mix of support with Anti Tank Missiles (Javelin), Engineers and maybe spotters.

I wish I would have the skills to make such a game... :D

Oh and no WW2 Shit. I want to drive M1A2 and Leopards 2, Russian Tanks etc.

Try to make something unique as The Ship

i think this will be pretty good and unusual thing to play

I like open world games where you can decide and make choices :)

Make Megaman multiplayer. PvP. No fps. Too many shooter game nowadays.

There aren't nearly enough games set in the old west... Could be a simple versus mode or defend a town mode (think Magnificent 7). If you want a shooter that is.
If not even better but I don't have any worthwhile on ideas there. :D

Stealth games we need more stealth games... like the multiplayer of splinter cell (3 and 4), that´s for a Co-Op game

and for a multiplayer a third/first person fast paced + loot + level system (imagine a Borderlands meets Bulletstorm); against mobs.... is there any source based MMO?

Co-Op / Versus game, Helping each other to win, CPU's or other players

Going to bed now, exam tommorow, haha, i'll reply later.

Usually my main issue with multiplayer is that internet connection can be a factor. Lag and delay can really ruin any game experience, especially in fast paced games. Turn based games seem to effectively neutralize that(I'm thinking something along the lines of "Might & Magic Clash of Heroes" which has an interesting, unique and, most importantly, relatively balanced combat system). Of course this means trowing the actual experience/level system and realism out of the window, no fast paced action and some serious effort on balancing the game. Also, I don't really understand how the source engine works(I'm still a novice programmer at best) and what exactly makes it different from other engines, but it doesn't seem to be very appropriate for turn-based games which usually require a sky view of the battlefield instead of an up-close detailed view. But, well, that's my opinion on multiplayer games, don't know if it helped or not. ;)

Maybe a metroid/megaman styled game in first person. Team deathmatch maybe with lazer guns and energy swords?

You have a Type 40 TARDIS.
Do it Jonathan.
Do.
It.

Just look at that awesome old good Gameplay of Rune! That's what I would like to see in your new game!

my idea of the best concept of a multiplayer game is a multiplayer game that doesn't have the problems of a normal multiplayer game.

Implement a check so that every time you speak with your microphone, your voice is analyzed. If it's too childish or sharp, then the microphone mutes.

Competitive pure Steampunk survival FPS ? Imagine a Killing Floor round based survival with 2 teams of players trying to survive waves of steam golems and other contraptions with harpoon guns, steal assisted launchers, industrial era weaponry. All the while trying not to be taken by surprise by the other team while fighting the mobs.

Basically a perl level based game like Killing Floor with 2 kinds of levels. A persistent level per class which goes up doing class specific actions giving access to better weapon prices and stats. And a per game level that goes up with each kill / round survived that unlocks some weapons and accessories for the game.