If you're looking for something close to the tabletop version of 40k, Sanctus Reach is a good fit. It's generally close to the tabletop and has dozens of units from several key factions. While not perfect, it's still an enjoyable time if you have someone to play against.

Overall thoughts:
Gameplay: 7/10 - not bad, not great
Visuals: 8/10 - I quite enjoy the visuals for SR. The models all look good and the combat animations are a highlight. Map design isn't bad either.
Mission Design: 7/10 - destructible environments make a great addition to the maps, which are already solid. Missions are enjoyable in their own right.

I rate Warhammer 40,000: Sanctus Reach seven overpriced Castellan Knights out of ten. If you like 40k, you'll probably have a good time.