Pay full price to be a beta-tester or wait six months when it costs $20 and they have fixed half the bugs.
And let's not kid ourselves Steam is malware pure and simple. Have you seen the list of programs that conflict with it?
In short you will spend have your time trying to get the thing running and then play a game that is horribly easy with weak AI and constant bugs (trade routes, battle scenes land & sea, navy in the new world and many others).
Somewhere in there was a good idea for a game. Either Creative Assembly bit off more than they could chew, or they're just plain incompetent. Whatever...I hear Europa Universalis is good...