What is MINECRAFT for a game and what is so special about it?
Minecraft is a game where you can build things of all kinds with blocks of all kinds
The special thing is that not always the same thing happens, but you can build and change a whole world in single player mode and can be creative and in multiplayer mode, the developers are virtually no limits set, so there are, for example, mini-games in which you forget that you actually play Minecraft.
Just look at a few videos, then you'll understand what I mean.
A sandbox game, which means it depends on what you are doing with the game, basically there are two modes:
In Survival Mode, you must master all resources and defend yourself against numerous monsters that emerge at night, there's no real target but you can try to defeat the two bosses, the Wither and the Ender Dragon (she is female).
In Creativemode, you have all the resources unlimited and can let your creativity run wild, you can fly and you're immortal!
There are also thousands of mods on the Internet and again thousands of multiplayer servers, which are all characterized by their game modes that do not exist in the normal game.
The worlds are 30000000x30000000 blocks big and each time random.
But the best thing is, you look at a review on Youtube.
Because you can do so many different things. There are so many different servers with so many minigames. You can also download mods. You want to play Pokemon? No problem, PokemonMod. You want to play a mmorpg? No problem looking for a rpg server. You're into cs: go, be creative, pvp? No problem, everything is there
RentedDog3942 has explained the basic principle very well.
I have often heard the comparison with Lego. You can create your own Lego (Minecraft) world of stones. It just will not get boring, be it in the multi or the singleplayer.
But that's just one side of the coin for me. The other side are the servers. Not just playing on a server is fun, but a guiding. After Minecraft is more or less "open cource" you can program plugins mods etc. And make your own "own prigrammed / modified game" out of a "normal" game. You learn how to run a server, how programming works, what it means to support users in case of problems. You learn how to manage a server, how to handle planning with existing resources, and much more (etc.).
In short: Minecraft is a game where you can build your own world on your own or with others and that (in my opinion) never gets boring.
On the other hand, Minecraft is a game in which you playfully learn the basics of IT (programming, server engineering, project management / problem solving…) (if you help with multiplayer backups).
And exactly these aspects are what makes Minecraft so special. A true classic.