Very boring and disappointing.
Now lets see why this game got a 4.5 from me, I will be comparing Victoria 2 with Crusader Kings 2 which is a new game from Paradox.
1- Too boring, quite simply put.
More often than not you will find that there's nothing to do and you will sit there staring at the screen doing nothing for too long, Paradox probably didn't want this game to be too complex but that's what makes their games like CK II fun, its complexity and vast number of things to do. In CK II there's a lot to do but you're not expected to do everything, which adds a whole new layer of fun to it that Victoria 2 really misses.
2- Whatever you do, you'll never catch up.
Playing as an uncivilized country, if you manage to westernize before getting annexed by someone it will be already 1860-70 and you will be too backward in technology forever, now that's realistic because only Japan managed to really westernize but the problem is that if you already lost a province to any civilized country you might as well forget getting it back. Another problem with playing as an uncivilized country is that, again, there's too little to do, even less than if you played as a westernized country.
3- The game is too shallow.
Who would've thought! A shallow Paradox game? Now I know many people will disagree but just think about it: The diplomacy is from EU3 with very little editing, the economy is quite bland, wars have very predictable outcomes, rebellions are mindless and are only a nuisance if you're a tiny country struggling to increase your soldier pop.
4- Diplomacy leaves a lot to be desired.
This is a game about a century of mind-boggling diplomacy. If this game should be about anything, its diplomacy. You should be spending 80% of your time on a diplomacy table trying to get something out or just proving to the world that you exist. But that makes no appearance in this game. Even CK II which is about a time when you didn't even need a reason to annex a whole empire has a better diplomacy!
Victoria II has a sophisticated POP system that the game revolves around, which is wrong IMO, the POPs should be of secondary importance to international diplomacy, nationalism, and imperialism (which all fall under the diplomacy title). POPs aren't very well done either, you cant interact with them except through events and policies. So you cant do the divide et impera thingy outside an event... which, come to think of, are very repetitive and little in number.
Bottom line, don't buy this game. If you want a good and complex strategy game,Paradox-style, get the amazing CK II or wait for the upcoming March of the Eagles and Europa Universalis IV.