Hearts of Iron 3 at release was something of a disappointment. See the many negative reviews right here on Amazon for the details - slow, crash-prone and with a tendency to go hog-wild with the "alternative" part of alt-history. Things have gotten much better and I can now say without any reservations that this is a good, approaching great game.
What is HOI3?
A grand strategy game covering the World War 2 era from 1936, the year Hitler re-occupied the Rhineland and set Europe on the road to war, to 1947, the year after the real-life defeat of Japan. The player can choose to control any nation from across the globe, from titans like Germany or the USSR down to relative minnows like Liberia or Ecuador. The object of the game is rather fluid - certain nations are locked into one side from the beginning, but with many, including the USA, Italy and Japan, the player can choose to side with democracy, fascism or communism, or simply pursue their own military aims - although any amount of warmongering will mean you probably ending up in one of the alliances sooner or later, and the game, as a war simulator, will be very dull for anyone attempting to play a neutral, pacifist game.
What's the gameplay like?
Complicated, although there's plenty of optional automation. At your disposal are warfare (of course), diplomacy (generally focused on trading and on either gathering nations to your cause, or agitating to get yourself admitted to one of the big alliances, with a few other bits and bobs), industry, technological research, national politics, and espionage. All of this can be automated - if you want to play the low-level tactical game, you can assume direct control over every trade deal and troop movement. If you want to play the strategic game, you can turn on the automation for everything and just define general goals for your highest-level commanders. Or you can play a mixture, allowing the AI to handle all the diplomatic and espionage stuff while you march your armies around, or indeed vice versa. The AI is generally quite adept at doing what you want it to, although be warned that if you have your diplomacy automated while playing as Germany, the AI *will* press the "Demand Danzig from Poland" button that starts the War in 1939, regardless of how well prepared you are.
Troops are commanded in the traditional manner - you march them into a province, and if there are enemies there, then violence commences. Divisions are rarely destroyed through direct combat; they will fall back to regroup when their morale or organisation level reaches breaking point, only being completely annihilated if they have nowhere to retreat to - which makes encirclement a key objective. Air wings and navy groups are handled differently, being assigned missions which can scheduled and set to auto-repeat or not as you wish. There's also an "Order of Battle" system which allows you to set up command groups above your divisions, at the corps, army, army group and theatre level.
Partisans and resistance fighters are almost a non-entity; the game doesn't account for units smaller than three thousand men or so, so the most you'll see of them is the occasional provincial uprising, easily put down by any single division of your defence force. Another underplayed aspect is that beyond helping the German-American Bund or the American Communist Party grab power at the 1940 elections, which helps keep the USA out of the Allies, international political intrigue is of minimal importance for anyone - changing the party in power when a nation is already involved in a big alliance does absolutely nothing.
It's superficially intimidating, but you don't have to master everything on your first play-through - which is lucky, since you won't. Overall, it's very much more chin-stroking than heart-pounding.
What are the graphics and sound like?
Functional. The interface is mostly quite intuitive, although some things are in odd places - for instance, you enact national decisions in the Diplomacy rather than the Politics screen, and you create new theatres by building up a new chain of command from the bottom, starting with a division, rather than creating the chain downwards from the theatre level, which would seem more logical.
There's little flash. The map looks like a map, not ugly but not conspicuously beautiful either. The same goes for the units themselves; the default is counters which represent your units - sprites are available as an optional extra - and they do the job well enough but offer little in the all-singing, all-dancing department.
The sound largely consists of music from the slightly more bombastic side of classical, with sound effects limited to the informative - the occasional "Boom! Sploosh!" which announces that a ship has been sunk, or an oddly-chosen clicking noise that tells you partisans have risen up in one of your occupied territories.
How stable is it and what bugs does it have?
It's much better than it was. Paradox seem to have finally squelched a memory leak and speed issue that made the title more or less unplayable at launch, especially for those of us unlucky enough to have computers infected with MS Vista. Crashes still happen, but much less frequently - twice in a solid real-life week of playing for me, as opposed to several times per session when the title first launched.
Also worth noting under the "bugs" heading is the whole alt-history thing. Several progressive tweaks mean that the game has moved into the realm of the plausible - now, the USA won't join the Allies until the War is well and truly underway, Japan will probably beat China or at least fight them to a stalemate, and most importantly, Germany actually will start the war in Europe. Oddities remain, though; for instance, it's usually Italy who does best in the war in France; both the German and French AI will stack 95% of their forces along the Maginot Line, leaving the Franco-Italian border weakly defended and the German thrust through Belgium and the Netherlands under-manned. The net result is usually that Italian cavalry is galloping across Occitania while the German tanks are still bogged down around Brussels, and it's a 50/50 thing which of the two gets to Paris first.
Also, the AI hasn't really got much better at doing naval invasions or allied co-operation. Left to its own devices, the AI's attempts at D-Day are little short of pathetic; British, American and Canadian troops will show up in numbers of a few thousand at a time, usually months apart, attempt to land at a defended and garrisoned port, fail, give up and go home again. Playing from the other side, you obviously have the benefit of hindsight, and can start preparing your plan to liberate France three years before the war even starts, which obviously makes the whole thing rather easier than it actually was.
Overall then?
A deep, involving and (now) mostly bug-free strategy game, recommended to anyone who isn't turned off by lots of numbers and strictly functional, high-level-of-abstraction graphics. Bring a powerful computer because the CPU, not just the graphics card, is going to be working pretty damn hard tracking the manoeuvres of tens of thousands of units across tens of thousands of provinces, even without resource flows and international relations to throw into the mix.