To progress past the beginner stage you need to stop relying on tutorials, come up with a reasonably sized project of your own that goes slightly beyond what you know you're capable of and go for it.
As for MMOLike gameplay with unity, yes it is possible, the built in networking however is not suitable for it so you need to either use a suitable third party networking solution (Photon or smartfoxserver for example) or write your own networking.
Thank you for your reply, and that does make sense!
The problem I'm having, is that I always aim way too high.
Could you tell me a sort of game, anything, that would be suitable in this case?
What is the most advanced game you've made thus far ?
On the easy side of things you got simple arcade games like pong, breakout, tetris, space invaders, asteroids.
A bit harder but still reasonably easy would be 2D platformers (like mario, megaman, commander keen, etc) (There is quite a bit of room to add advanced features in a 2D platformer though)
3D shooters are a bit harder (if you use an engine like Unity or UDK the difficulty of a 3D game isn't that much higher than for a 2D game though since some of the most challenging parts are handled by the engine).
On the more difficult side you have games that require advanced AI such as strategy games, team sports games(soccer, hockey), etc and multiplayer games (MMOs being even harder than normal multiplayer)
Regardless of what type of game you're making though, don't aim for anything that requires large amounts of high quality content unless you can generate it procedurally. (Creating high quality content is insanely timeconsuming)
Honestly, I never made a full game. I only made small things that would be a part of a game.
Thank you for suggesting these things, It'll keep me busy for a few days.