If you know Dominions3:
Dominions 4 is an attempt to turn Dominions 3 wall-like learning "curve" into a slightly less steep one. Let’s say a "Pisa tower wall" curve!
A bit more seriously this game is just the a simple update of Dominions 3. However this one is the must have. Some new races, much more community support (no1 is playing Dom3), here you will be able to find people to play with. If you loved Dom3 do yourself a favour... If you don't:
This is a map-top-view war strategy game with races deeply founded on global mythological history.
It is like playing a mythological version of Risk (the table top game) in which each and every unit of yours has individual characteristics (stats, afflictions, abilities etc.) which are persistent through the entire match.
This will be delightful for people that love finding the most "efficient" routes to play, because you have so many variables to consider you will probably never be able to do so, but you will still love the challenge.
It will also be delightful for people that read lore. Each and everything you control (or don't) in this game has their characteristics explained in one or two paragraphs entwined with lore which in the end is mythology.
TL;DR: If you really usually jump for TLDRs don't bother getting the game.... there will be long necessary reading in the game and honestly you will need lots of patience to learn it! Otherwise... if you read the thing with a smile, buy it already.