Stop reading this, buy all the DOW games. Look don't ask just buy it, you won't regret it. In particular buy the master collection, i'll explain why below:
Why buy Master? Master comes with all the factions fully playable in multiplayer and single player skirmishes, that's why. Simply download, install and play all of them at least once and you have full access to everything. You get 9-10 factions all together, 9-10 factions that all play /very/ differently with their own fun and unique tactics.
so look i'll do a review just for fun, but hurry up and buy it, you won't regret it:
Fun open campaign: None of this boring DOW:II campaigns where its "OH LOOK ITS THE SPACE MARRINES WE'RE SO SPACE MARINEY"
Diverse factions: Space Marines, Imperial Guads, Necrons, Tau, Eldar etc don't play alike, at all. They each play very differently and are relatively balanced. Try them out they're also all flavoured differently so if you're into BDSM I suggest playing Dark Eldar. If you're a pyromaniac who loves girls with big guns, may I direct you to the Sisters of Battle. If you're a ♥♥♥♥♥ I will direct you to the Space Marines. If you're a ♥♥♥♥♥ with some angst I would direct you to the Chaos Space Marines.
Multiplayer: By gaming standards this game is old, but there is still an active multiplayer community, thats more then DOW:II can really say.
Army Painter: Ever look at your GLORIOUS IMPERIAL GUARD WITH BALLS OF ♥♥♥♥ING STEEL and say, gee they look stupid, they NEED TO BE ♥♥♥♥ING PINK, well guess what: You can customize the colour schemes for your army, if you want to create an army of Pink Necrons or Imperial Guards from the Planet majesta then go on ahead and do it.
Replay value: This game has a lot of replay value in multiplayer and campaigns.
Graphics are a bit dated, but thats okay, it means it can run on your rig.
the multiplayer can be difficult at times, i've lost sometimes very fast.
NO Tyranids. I think there are mods that fix this but I don't bother with them, I hated the Tyranids in DOW:II OP AS ♥♥♥♥. This might be a pro, idk.
Guides are currently "Meh" on the steam community section, most of them being troll guides.
Some SPESS MEHREENS (Space Marines) chapters are not represented beyond some pre-made skins for them. So if you're expecting to bring out some Space Wolves the best you'll get is some light blue power armour for your SPESS MEHREENS. But, who cares they're SPESS MEHREENS.
Final notes: IF you're still reading this you're wasting your time when you could be burning the heretics and slaying the Xenos in the name of the EMPRAH. But in all seriousness Soulstorm is a recommended one to buy along with any other expansion as soulstorm is where peep's go to play multiplayer. But Soulstorm only comes with Dark Eldar and Sisters of battle. See other expansions for their factions. Or buy the Master collection.