The beauty (and demise) of minecraft is the sandbox nature of the game. You don't have to have an endgame to have fun. (And the latest additions to MC has been really bad in that regard, now it has created an arbitrary end game)
The demise part here is, there is no goal for new people, they have to figure it all out on their own. When they finally realize that there isn't really an end game they get confused because they are used to have a plot, a main storyline to follow.
God forbid if they had to make one up on their own or challenge themselves in new interesting ways.
Think back to when you where a kid, did you and your friends come up with new ways to play that game outside? Where you playing indians and cowboys and picked up ever more interesting sticks that resembled revolvers and rifles and shotguns?
Did one of you suddenly pick up an odd looking stick and call it a ray gun or phaser? Did one of you leave his role as an indian and instead turn into chuck norris or an alien or a cat?
You see, imagination is a good thing. You are not supposed to be ridiculed for being unique and coming up with new ideas. It is to be encouraged!
Minecraft is a huge playground for kids and adults alike to re-live (or reinforce) that mindset. Instead of following all the rules, you make them up on your own as you go.
Now, i am not saying that is fun for everyone and sometimes it's good to have a set of rules to stick by. The introduction of hunger in Minecraft for example gives you a default challenge that you have to overcome on harder difficulty levels.
Mobs are a constant enemy that if they didn't exist, would make the game dull rather quickly.
And that's where my suggestion comes... Find a server (preferably with a few friends) that has PvP enabled and start a war. Fight for your resources!
It does help to alter the ore distribution so that valuable resources are hard to find and far between. Enter the "gold rush" era of the 1800's and lay claim to land and shoot (or stab) any intruders that try to steal from you.
All depending on how good your imagination is you will eventually find yourself in a great game experience, a non stop real time strategy game.