There is just no other game like it...
Since 1995 all other RTS aimed at getting more "realistic" they hid the Grid they made animations smoother and graphics more believable.
They simplified the strategic value of space and worked to lower latency and the in game delays and time (ticks) thus favorising a more reflex/speed based experience but in the way I feel they lost the game part of the products they were creating...
War2 is a game and it was created with the gameplay in mind first and foremost and it transpire when you play it every unit has its place in it not just because it was "cool" to have it there but because it truly did something others do not do as well.
Every single unit in the game is there for its strategical value, it is thus clear and simple to get into and yet so satisfying to play.
In war2 the space matters to a whole other level than any of them new games every single tile matter, placing your tower one tile off may mean its death and it is true for every single unit in the game.
The tile every single or your units stand on as well as the areas of the map/terrain they allow you to control is what makes war2 such a unique and amazing game.
And there may be many other reasons but as for the game itself these have to be the main reasons I keep coming back to war2