Dave's right usually a few super powers start emerging and then the snowball gets underway. The map changes pretty dramatically from game to game though. I've seen games where Luneburg (a one province minor) took over all of Germany. You just never know what will happen. So, the game doesn't get repetitive.
Having said that, the game does have a "Lucky Nations" mechanic. These nations historically were power houses. To reflect that, certain countries get stat boosters to ensure they perform as well as their historical counterparts. So USUALLY these countries tend to do better (France, Austria, Britain etc).
This feature can be turned off or randomized, but I think it has to be set to historical for Iron Man games (for achievements, can't reload from earlier save).
Here is a post detailing that mechanic.
http://www.eu4wiki.com/Luck