Rating Halo Wars is a bit conflicting for me. I think its pretty lackluster as an RTS game, missing many mechanics and features that are standard for the genre. However, this absolutely FEELS like a Halo game, they absolutely nailed the atmosphere and uniqueness of the franchise. If you like the Halo universe, and you just wanna experience it from another perspective, you will enjoy this one.
If you want a solid and competent RTS game, maybe just play the campaign and look elsewhere.