CK 2 is not exactly a great strategy game though, traditionally speaking. If your main goal in the game is to conquer as much territory as possible, then there are better titles for that with deeper strategic possibilities, resources and so on. Despite of the recent additions to the combat system, the war side of the game still leaves a lot to be desired for. The most common and fool proof strategy still is the good old "get a huge mob, beat the enemy's huge mob with it and then go win the war."
Also, as far as strategy goes, Crusader Kings is highly random. There are frequently
whole threads on the official forums about "the game screwing the player over" because someone's carefully planned strategy was ruined by a simple random event. And contrary to what people claim, the AI is actually pretty smart. If it sees it's going to lose its kingdom to you through bad inheritance, you can be sure it does everything it can to prevent it. And often succeeds too, if you are not careful enough.
I'd say the game is wonderful, but its charm comes from something completely different than what it looks like on the first glance. I take it more as an RPG and a political game than an old fashioned grand strategy. Whenever I start playing it like a latter, it becomes stupidly dull.