Great fun, strangely addictive, though the AI and pathfinding will aggravate you and the mechanics bamboozle you.
The game doesn't look that amazing, which an interface more in line with late 1990s games than now, but it is easily enough to do what it needs to do. There is a lot of different things to learn and absorb in this game, and the manual and tooltips do an okay job at explaining things, though even on my 4th playthrough there are still things which I don't fully understand. The diplomacy and combat are somewhat basic, but once again enough to do what you need them to do. The AI can be absolutely terrible though. One clear example is setting your troops to hunt rebels, it's not uncommon to find one of your regiments coming from the other side of the continent to put down a revolt (which happens a lot in this game) thus leaving it's area completely unguarded, and sure enough, rebel pops up, no damn defense. To add insult to injury, the incoming unit will pass through unclaimed/enemy/allied territories instead of sticking to your own, resulting in losses due to attrition, or native attacks. The pathfinding of your ships is also atrocious, the number of times it will decide to cut across open ocean or detour out there for no good reason when it could stick to the shoreline and suffer no damage is maddening.
Another good aggravation is the number of messages you will receive if you stick to default settings, a lot of the times the messages are completely useless to you. "X refuses to allow to use their centres of trades!" I have no merchants in their CoTs, and they're so pathetic I wouldn't trade in them anyway...
"X is embargoing Y!" I care because... "X has made peace with Y" Great, they're both Indian countries and I'm landlocked in Europe, I care because... "A level 1 advisor has appeared in your territory!" Great, a pathetic advisor that I wouldn't hire, even if I had all empty seats... etc etc. While the game does a good job of letting you modify the messages you get, it doesn't allow you to sort by degree, eg you might not care about a level 1 natural scientist, but a level 6 statesman you'd definitely want to know about, but no, you can't specify a level above which you'd like to know if they're present, or that you can't keep an eye out for say a land reform specialist of any level but you don't give a damn about yet another level 1 navigator. Or more importantly, you don't care about the 300th victory against rebels your troops have had, but you do care if they suffer their first loss. So you're going to have to choose between getting a lot of useless messages which simply don't matter to you or missing out on important information (which, if you're like me, you might miss anyway, as you're just trying to clear the junk you miss the important message).
In spite of those aggravations there is something strangely compelling about EU3, and it will take up a lot of your time once you get into the swing of it. As it is a budget game now, definitely recommend getting it.