I'm probably the only person still actively playing X2, so I'll definitely vouch for it.
I remember playing Freelancer and having a great time, but always wishing it was a deeper experience. As in: owning property and fleets of ships. The whole "one ship at a time" thing felt extremely shallow.
X2 gives you that in spades. believe it or not, I've probabaly played 150-200 hours by now and I haven't even finished the main plot. I sort of abandoned it to become a mogul.
As far as space combat goes, Freelancer is a little more smooth and arcadey. X2 has a stiffer flight model. I still have fun with it though. It's very difficult and very satisfying to defeat a larger more powerful ship. To do so you pretty much have to have missle equipped wingmen, though.
Shit in X2 is EXPENSIVE. You'll play for a long time before you get powerful ships and own a bunch of factories.
One of the great joys of X2 is figuring stuff out. Ex. - With the exception of Freelancer I was new to the whole space sim genre. So when I finally bought some wingmen I only purchased enough speed upgrades to allow them to keep up with me. My novice ass figured speed upgrades are expensive, and would be wasted on escorts.
But they kept on getting blown up during battles with F3 class pirates; I simply figured I wasn't strong enough to take out certain ships. But then it dawned on me: my F5 wingmen's biggest advantage is speed; If I limit them to my F4 velocity they're sitting ducks. The next time I purchased new ones I maxed out their speed. The battles against F3 class ships were still tough after that, but I started winning some of them. As I said before - very satisfying.