Oh golly;
I think one of the top things that brings people in(including myself) is the fact that they have to ways to play: Survival and Creative.
Survival is exactly how it sounds. You have to find resources to craft and survive. The First thing you'd want to get is wood to make a crafting table to make tools(i.e. a pick axe) to get even MORE resources.
In survival you also have to find food for yourself; there are numerous ways to do this! Fishing, killing pigs or the chickens or cows, etc.
But thats not all those animals are for. You also have horses, wolves, jungle cats that you can TAME by using certain items and then with horses you can ride them.
There are also a whole bunch of other animals.
Creative is where you go straight in and you have EVERYTHING already. All you have to do is hit the button for inventory and just type it in or scroll. So many people create amazing builds.
And people actually make some creative videos as well, if you'd like I could link you to some.
Another thing that makes Minecraft so great is that there ARE servers(yes they cost money sadly to create one). I am currently apart of a server called mineplex where you play all sorts of different minigames with other plays.
And one last thing; you can customize your character with a skin. I can always show you mine to show what I mean.
But really. There is just a whole lot that is great about minecraft.