It’s an area of control game where you build a map of islands out of tiles, occupy those tiles with ships and soldiers and openly attacking each other. Plus you have God cards that let you break the rules in different ways.
While Hellas is a fun game in general, the reason that it stood out to me when I first found out about it was that it was a German Family game that had direct conflict, literally combat. At the time, merging the sensibilities of war games and German Family games was pretty unusual.
Of course, that also depends on what you’re willing to consider a war game. When folks are willing to argue about whether or not Memoir 44 or Twilight Struggle are war games, Hellas is on super thin ice as far as being considered a war game. (Is chess a war game?)
I spend a lot of time thinking about the different design schools of games. And I do think they are important because they help explain what the goal of the design is, what the intended audience is. To be fair, I think it’s much more important for publishers than for consumers.
BUT games like Hellas (and Memoir 44 and Twilight Struggle and many more) are examples about how porous these labels are.
I do believe that there is real value in defining games via design school, in particular from a marketing standpoint. However, there is a definite danger in letting that be the defining characteristic of a game. That is far from the end all, be all of games. If you (or I or Bryan down the street) let that be what makes your decision on a game, you might be in a game cult.
And more and more, game designers take inspiration from different schools for one game. Designs schools are tool boxes, not limitations. Hellas is an example of that from 2002.