Had this borrowed from my brother, and just started playing it regularly in the last couple weeks. Awesome game.
I go to MLS matches, but I don't know a whole lot about soccer...
Definitely a steep learning curve. I'm only playing on semi-pro and find it sufficiently challenging, and I'm still messing around with which assists I want on and which I don't. Passing assists I generally leave on, shooting assists I generally turn off.
I don't see what the big deal is with headers, I'm about 20 matches deep into my first season playing in the Scottish league, and I've put in 4 headers with my virtual pro (6'0" striker) and got the assist on three more so far with the cross.
Defending is great, ball control is great although I'm still learning how to put special moves together. Definitely one of the best sports games I've ever played.
Also, kind of my main point to bump this thread, the Euro 2012 expansion should be coming out soon and will have all of the UEFA national squads. AWESOME.