I bought it because some of my diplomacy meetup friends play it a lot, but honestly? I found the game to be a bit overwhelming in terms of scale and scope. Not really sure what half the things do, and being unable to start with a clean slate (like in Civilization) makes it really difficult to learn. But I'm guessing if you know the series, and have played it, it probably isn't so bad.

It has a lot of good points, and some not so good ones. It's a lot easier to learn than EU3 though.

Each of the four EU III expansions made it impossible to play the old version given that they all unquestionably improved important aspects of the game (realism, playability, reduction of uneeded annoyances, etc.). Many EU III patches contained similarly dramatic improvements. Is EU IV a similar sort of improvement? I see the graphics are better, but I don't know what else has been changed.

I haven't played it myself, but they have completely redone taxation, merchants, diplomats, advisers and many other aspects of the game. I'd check the dev diaries for everything they did.
http://forum.paradoxplaza.com/forum/showthread.php?631266-Europa-Universalis-IV-%96-Developer-Diary-1-%96-The-world-is-at-your-feet

@Onar - yeah, that's the EU franchise in a nutshell. I find it much more rewarding than Civ, as many aspects are superior to what Civ 5 has to offer.

EUIV has the Crusader Kings II style large patches & smaller, more frequent, DLC's approach. So if you don't have the DLC you can still play multiplayer as each of them can be turned off.

First DLC since the pre-order bonuses is coming out in a couple of weeks.

It's improved trade dramatically on EU3 and also has a lot of neat ideas and changes like National Ideas being a lot more critical and unique.

At the moment it punishes growth a bit too much for me though, but I think that's being changed in the patch that's coming out with the new DLC (which also looks pretty awesome).

EUIV is a massive improvement over certain issues in EUIII, and the whole research system has been overhauled to make it easier. I've been playing Paradox games for several years now, and this seems to me to be one of their best. Also, implementing Crusader Kings II style graphics has made it more visually pleasing overall

EU4 is great. Better than 3. Still liked CK2 a bit more.

I like CK2. Is that an almost guarantee I will like EU4 or are they very different?

I understand it's about factions instead of characters.

Trade is probably the greatest mystery of EU III to me. It's good to hear that research was overhauled. Does EU IV really punish expansion more than EU III already did?

Are any features lost?

It's not that EUIV directly punishes expansion, it just causes research and stability to take a massive hot since coring of provinces in controlled by the same 'monarch points' which control research and stability, and you have to choose in which category you're investing your points. And the larger you are, the more the coring cost per province

I bought EU 3 from Steam a couple of years ago. Without the time to devote to it, I found the learning curve steep. I come at this as a fan of strategy board games and the Total War series, particularly the first Medieval series (including Viking Invasion). I like Civ V, but I find it a little "too" gamey. I think I'll give EU 4 a look.

Trade is still mostly a mystery to me in EU4. There are great forums though and people have crunched the numbers. If you want to understand it, you will.

I guess it does punish expansion quite a bit. It's easy to rack up "Aggressive expansion" penalties for taking more than a couple provinces per war, and huge coalitions can and will form against you if you continue to be a bad boy. I like it this way, though. I hate blobbism for the player and anybody else and always have felt that endgames in these are always terrible because (EU3) nobody can mess with you, and most wars are just not worth fighting for the reward or (CK2) rebels rebels stupid rebels. Anyways, EU4 does take a step in the right direction for making the game more enjoyable throughout. I

I think the issue isn't the huge coalitions, they're fine. It's just that at the end of a 5 year war against a coalition of half the world you can take all of 3 or 4 provinces...