Halo Wars is a great idea, get the rich universe of the Halo francise and give it a classic RTS remix. For the most part it works out great, the battles are quick, intense, and the controls hold up the entire way through. Unfortunately the more time you spend with Halo Wars the more you realize how little there is to enjoy.
The campaign lasts 15 missions, covering a wide variety of RTS play styles and unique objectives to accomplish. Despite that the campaign isn't all that interesting and, because of how simple the game is, isn't all that important in terms of practice.
The problem with Halo Wars is that it's just to simple. There are only two factions, one win condition (kill the enemy), and the tech tree is more like a tech fern (puns!). Still if you love Halo or are new to the RTS genre Halo Wars is a great buy. However if you are an experienced RTS player then either pass Halo Wars up or wait for a price drop.