I like this game. It's a simple to learn game with plenty of tactics involved. I'd consider Strategic War in Europe a good introduction into the Grand Strategy genre.
There's a decent variety of units, all of which can either be leveled through battles, or you can spend extra in training them so that they come out at the level you want. There's a basic research and diplomacy which I found a bit disappointing, but I still enjoyed the game.
There are several small bugs in the game, UI mostly, and compared to Paradox Interactive's Grand Strategies, the visual map and map modes are bare in comparison to put it nicely. But it's not a game breaker. They do offer 2 map skins and 3 unit skins, so there's some customization there.
Overall, I think $15 is a bit much considering the bugs and lackluster map modes, but I'd still recommend, since it's a fun game. I'd wait until a sale, $5, maybe $10 at most.