its great, I played Dawn of War alot - and I feel this is one of the best expansions I own. It not only adds an entire new race (imperial gaurd) and a new unit to the existing, it also rebalances most of the game with things they must have just been too scared to do through a patch.
Much cheaper units, more research to unlock certain things. As an example the terminators were always complete crap, cost 2x the squad cap of a space marine squad, cost a hell of alot more...so 2x space marine squads (working out to the same price) would have a better variance and better chance of not breaking to just make terminators only worth it if you happened to think they were cool or something. Now cost +1 squad cap over the space marines and are much cheaper.
One thing they were trying to achieve was to make games actually lost longer than 10 minutes online, as it would basically be whoever wins the rush or spams the most inane unit early on would win quite quickly and that would be that. I haven't tried this online yet due to not having the internet in my uni place, but to me it still feels like it takes the same amount of time to tech up to later levels (in some cases longer due to new thing to research that take more out of your build order and leave you teching a little later on) so im doubtful to whether or not people are getting that far.
still great mod, excellent support from devs who not only want to fix the main bugs, but have said in interviews how they are committed to keeping the franchise going with more expansions / new game altogether and how they want to see this in high skill level competition so a garuantee that they will strive for balance perfection no matter how many patches it takes.
Dan