I'm more fond toward Dawn of War because of the familiar cover system (From Company of Heroes) and it's emphasis on the tactical components of an RTS (Making it an RTT), without the need for crazy korean actions per minute.
I haven't touched Shogun 2 or any of the games in that vein.
But I can say as an avid Relic and 40k fan, that Dawn of War 2 requires an adjustment in your expectations. Company of Heroes it is NOT, in many many ways. Terrain is less nuanced, cover is less important, the game is much zergier, and the emphasis on heavy weapons and 'splosions means the game is more about sustained, overwhelming firepower (and well-timed click abilities) than it is about capitalizing on terrain advantages (which DoW 2 makes a token gesture towards, compared to CoH where every part of the map created tactical considerations.)
The game is "fun" and has all that meta-RPG stuff going, which is good. But the gameplay itself feels pretty mindless, especially the SP. Maybe it's the smaller number of units, maybe its the persistence of your characters, but I don't feel like I'm in the middle of a war zone in DoW 2. I feel like I'm playing through a bland action novel set in 40k. The challenges come in the form of unique-ish boss fights, and the occasional concentration of emplaced enemy heavy weapons which will ruin your squad (and your score for the level, which means less experience for the mission.)
So really, I think Shogun 2 is probably a better buy. DoW 2 does have MP, but you have to like the system its built on to enjoy it, and I really don't. DoW 2 pretty much felt like a shallower game than CoH, and about as deep as DoW 1. The only thing it rises above those two titles in is the campaign meta game, which any RPGer will like, and the graphics. But considering those are two things I DONT actively look for in RTS games, DoW 2 has felt like a big let down to me. You will not find the kind of deep, protracted fights you could get into in CoH, in DoW 2. They simply don't exist.
Its much faster paced than Total War.
To the point where defense is non-existent. That's why I hated the MP mode for DoW 2. It's about every player circling the map with a horde of guys, avoiding any defensive positions, to strike at your teleport platform. I could spend 4 hours playing a skirmish of Company of Heroes, creating artillery emplacements, mine fields, barricades and crazy ass defensive positions, before I even deigned to go on offense. In DoW 2, if you're not attacking, you're wasting time. Just way too frantic. Hence why they came up with the stupid moniker "real-time tactics" as opposed to "real-time strategy."
It's even enshrined in the SP campaign, where you you get graded on how well you did in the mission. On average, if you want maximum performance for the level, you have to beat it in under 10 minutes. They literally envisioned DoW 2 as a game about storming through tons of enemy positions without stopping. Which is fun for about 2 levels.