The game starts with you taking control of the Heir of the Covenant who wakes after a long slumber after missing the world war of which was his job to stop. In his absence though the world banded together to banish the threat and save the world from its recurring destruction cycle at the hands of the Arch Demon. The story is rather complex. I find it to be a wonderful story and so I think limiting the spoilers is needed.
They constantly add new features and content but you will find all your normal gacha trappings here:
Story mode with regular updates
Side events every couple weeks or so
PVP - Real Time is still beta but there is also the traditional fight other people's teams in an offline manner
Decent summon rates - there is a pity system in the game for new banners and the rates are on par with the other big name gachas.
Each of these generate rewards or currency and some are quite liberal with the amounts. One of the things that keep many of us in the game, other than the beautiful animations and story, is the fact that this company tends to be very liberal with rewards. The game has a starter plan to follow that gives great gear. Overall I think the tutorial series for the game is above average for the genre.