This review is written with Total War players in mind. As such, it will not adress basic gameplay that is inherent in all Total War games, such as turn based production and real time battling, but rather will compare Empire: Total War with other Total War titles.
As a Total War fan, my personal preference goes to this title, Empire. I like most Total War games, but Empire stands out to me. For one, I enjoy the historic time period. For two, it plays the most 'different' from the other titles.
Older titles, such as the first Rome: Total War game and Medieval II, heavily favour an agressive play style, with a lot of chaotic melees. Later games, such as Rome II and Shogun II, lean more towards a balanced stance between agression and response, depending on how superior your battlefield position and force is.
Empire: Total War, in contrast, is a game of patience. Instead of charging into melee, the gameplay entails meticulously positioning lines of infantry and laying down volleys of fire. Mirorring the idea of the age, it is the 'gentleman's edition' of Total War. The Fall of the Samurai expansion to Shogun II comes closest to the Empire style of play, with rifle armed infantry and gatling guns, and keeps the option to go into melee samurai charge mode, but Empire remain the only edition (excluding Napoleon: Total War) to favour a line to line exchange of fire.
Another difference is the naval battles. Granted, later editions in the Total War series incorporate these as well, but Romans or Edo era Japanese boats firing on one another with arrows pale next to the awesome power of a multiple deck ships of the line wailing away at one another. Again, Fall of Samurai introduces ironclad ships that approach this somewhat.
Of course, later titles have more recent, better developed versions of some of the aspects of Empire, and there are some other downsides to Empire. As usual with a Total War title, Creative Assembly has a tendency to leaving things not as smooth as they could have been. Most bugs have been smoothed out after release, as they usually are, but some small problems remain here and there (such as batteries of cannon simply not firing unless directed to do so in a very specific way).
Additionally, while the battles themselves offer some of the most unique Total War battle experiences, the map campaign improves little on previous editions. Not that this is necessary, because the region based resources and capture cities work well for the entire series. However, there is one significant improvement to me here, and that is that the map spans the most territory of any Total War game. Where Rome II limits itself to Europe and North Africa, and Shogun II is set in Japan, Empire scopes the entire Western dominated world of the Elizabethan age: Europe, North America, Africa and the Indies. The later release Napoleon: Total War does not nearly reach the score Empire does, and its campaigns are focused on smaller scale conquest rather than the world theatre of Empire.
As for the research system, it seems that the Empire title marks the start of an overhaul, where the series starts mimicing the more traditional 'tech tree' idea that prevails in many strategy games. This is not a bad thing, but it is an addition that was perhaps not entirely necessary. All the more so because sometimes it seems like a shoehorn to introduce the game's traditional late game obstacle. Every Total War game has some sort of hindering mechanic that makes the game prgressively more difficult as time advances. In Empire, research (which you need to keep up with your modernizing rivals) introduces squalor, which makes for an unhappy populace, which makes you either have to sink money into keeping them happy or have to deal with rebellions.
If you prefer a more agressive slugfest in a game, I would suggest Rome II, Shogun II, or if you don't mind some more antiquated aestethics and graphics, Medieval II.
If you like your games new and crisp, the more recent titles are sure to be your thing as well. If you want a more modern game that still uses line infantry and gun batteries, Shogun II's Fall of the Samurai expansion is your ticket.
But if you want a true, professional standing army of line infantry that knows how to hold under fire as well as deliver it, if you want to be a gentleman general of standing, if you want an 18th century battlefield, then this, my friend, this is the game for you.