I really enjoy Empire. Or at least the Darthmod version of it. The vanilla version, while fun, was immersion shattering. I didn't know that 18th century muskets used tracer rounds! The Darthmod makes battles much more realistic and satisfying to fight. I also appreciate the scope of the game. With a few exceptions, the game spans THE ENTIRE WORLD. No other Total War game has that kind of scope.
The introduction of the research and development system for both military and civil means is perhaps my favorite aspect of the game. No longer are your unit production capabilities limited by how big your cities are. It really feels like you need to work in order to make your units better. People may say that the troop types (infantry, artillery and cavalry) lack the variety of past Total War games, especially Medieval II. While that may be the case at the outset, researching technologies can make these same units fight in different capacities (Bayonets, fire by rank, square formation, etc.). Another complaint is that the styles of battle are the same for any battle. Two lines of men fire at each other until one runs away, each and every time. But isn't it the same with almost all battles in Medieval II, with the notable exception of factions like the Turks and Byzantines? Two lines of men charge into each other and hack away until one side runs away. Almost every time.
And the sea battles. My God, the sea battles are fantastic! Any inconsistencies with sailing against the wind have been corrected in the Darthmod.