Diplomacy is a satrategy game, like Hearts of Iron. But there isn't WWII, it's WWI.
If you have played one of two Hearts of Iron games, you'll enjoy this game. It has similar gameplay movements like Hearts of Iron series. Similar graphics, similar controls, and similar gameplay...
The game has very strong AI and if you make a mistake or something not good for you, enemies around you starts attack on you. You can make peace or nonagression aggreements between a country and yours, so you can be more powerful. The strongest country I see in the game is Russia. Russia has four pawns in the beginning of the game, the others have three.
Diplomacy is a good game. High gameplay and strong AI make the game better. If you have played one of two Hearts of Iron games, you will enjoy Diplomacy. Everything looks cool but graphics and sound. But these aren't important in any game like that. You will enjoy the game, trust me.