Poor documentation caused me to look elsewhere for game mechanic info. Started off interesting, but got tedious.
Computer Specs
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Intel Core i7 860 @ 2.80 GHz, 8 gig RAM, Radeon HD 5850
Documentation
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I actually enjoy reading the manual for a new strategy game. Digging into how the game works encourages thinking about how to approach the game. The manual for Empire is definitely under developed. It covers some basic 'how tos', but not much else. I couldn't find information on basic game mechanics, such as how the economy works. This is a moderately complex game so the documentation should cover the mechanics of play, otherwise making intelligent choices is difficult. Fortunately there are many helpful guides on twcenter.net and the official Empire: Total War forum.
My Game Setup
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Austria-long campaign-medium / medium difficulty.
The long campaign is from 1700 to 1799, two turns per year. A 50 year campaign is also available. The two standard campaign types awards you a victory if you meet some conquest objectives. There is also a prestige campaign where you try to build up the most prestige. These are points awarded for military conquest, research, and some other criteria.
The Early Game
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The first 30 turns or so were interesting. Making the choices of what to research and how to develop my regions was enjoyable. The battles stayed somewhat small (less than the full number of units one general can manage) so they didn't take very long.
The Mid and End Game
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Once my empire started to grow the game became more tedious. Empire doesn't present information in a very usable way for empire management. Research choices become a hassle because it is tedious to collect the relevant information. Do I improve the metal working or the pottery techs? Well, I would like to know how many of each building my empire has in existence, whether they are prosperous, how much money they make, etc. There is no empire summary screen to see this information. You must either scroll around the map counting or use the arrows to jump to each town one at a time. Either way isn't ideal. If there is a more useful method, please let me know.
The battles...
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To me the battles stayed interesting when they were on a small scale, such as 3 to 10 units per side. After that they became more of a chore to me. Obviously this is just a matter of opinion and if you enjoy the battles more than I do you probably will enjoy the game much more than myself.
I also found the same basic tactics worked for me the entire game. In general I could set up my units in the corner of the deployment area. Usually I would have a modest amount of artillery (1-3 units). I would protect the arty with line infantry and have same cavalry to help mop up. I don't remember losing any battles during the campaign, but I do think I lost one or two.
It seems like the AI usually brings the battle to you even when you initiated the attack. This let my defense technique described above work. When he was vastly outnumbered he tended to hang back, but if the forces were close in number he was usually the aggressor.
The AI does not do a decent job attacking a fortification. It does use artillery to soften up the fortress to create some holes, but with some well placed units you can defend your fortification even if you are vastly outnumbered. His troops usually don't all arrive at the same time, so you don't need to handle a massive attack all at once.
I only had one naval battle in my campaign since I stayed focused on Europe.
Diplomacy and Relations
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I am not going to describe in detail how diplomacy works, but I thought there was a good number of tools you can use to manage your relations with other countries (you can exchange technologies and regions, open trade routes, make alliances, etc). The reasons for a good or poor relationship was detailed nicely in a tool tip for each country. There were a couple things I found odd.
Countries seem to forgive your territorial expansion pretty quickly. I had mine up to a -40. When I looked at it again, it was in negative single digits. I did play fairly aggressively, conquering half of the Ottoman Empire right from the start. When Prussia and Poland-Lithuania attacked me, their lands were added to Austria's growing mass.
Also, when you do not honor a treaty when an ally is attacked it seems like it angers your former ally no more than other countries. A greater penalty with your former ally would make more sense.
The Visuals
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I think Creative Assembly did a nice job on the map. It is pleasant to look at and the information is pretty clear. You can view natural choke points pretty well. To me it was occasionally difficult to notice where an army's route could be blocked by terrain. The waypoint for units is color coded, so you can see how many turns it will take for the unit to get to its destination. Region borders are color coded so you can see if you border with an enemy, an ally or a neutral country. I would have liked it if it were easier to pick out my country's border as a whole. You can use the mini map to see this, but something on the campaign map would have made it a little easier.
The battle visuals are nicely done. The units have good detail to them, the terrain looks nice, and the smoke effects add some character to the battles.
There were a couple of battles where the frame rate dropped to a crawl. As I mentioned above, my specs are pretty good and I didn't have my settings maxed. This rarely happened, but when it did it was pretty bad.
Summary
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Stronger documentation would have been much appreciated. A player shouldn't be required to seek information from 3rd parties for basic game mechanics. An enjoyable early game gives way to a tedious mid to end game. The last 50 turns I turned off viewing the AI moves and hit next turn constantly. I was so far ahead I wasn't motivated to play beyond reaching my objectives. I was bored of the battles, so I didn't want to slog through any more. In fact I did auto resolve the battles once I had an overwhelming force.
It doesn't appear that each country provides a substantially different experience, but that is just a guess. I think playing a naval country like England would be very different from Austria, but beyond that I think the experiences would be similar. I actually have a thread asking more experienced players about this, so I may be wrong. I think if you enjoy the battles more than myself you can get a lot more replay out of this game.
Overall score (1 to 10): 6
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I don't regret the time I spent with it, but I don't feel terribly inclined to play again. I think if you enjoy the battles, you can easily add another point or two to the score.