It's difficult not to appreciate the class of Cossacks. Its gameplay focus is well split into all the aspects that characterise an RTT game: game rhythm, upgrades, buildings, unit variety and relevance, population realism, battle simulation... One has got to admire the effort put into crafting the unit functioning and overall building management in this one. Superb.
Cossacks offers plenty of pleasurable elements. First, there's the outstanding number of nations, each with its own architectural identity (wonderfully done, by the way); as well as the outstanding number of unique units and their precise importance on the battlefield or in the development of one's domains. Second, there's the realistic representation of population growth, with civil infrastructure costing you more as your settlement expands, although there is no set limit for your population. Third, there's the artillery/infantry details, amazing to watch as they engage in battle. Fourth, there's the customisable gameplay, as the options for a skirmish match are reasonable (type of terrain, type of elevation, game speed, resources, etc.), gathering all the good and fair choices everybody should have when playing a free-build or skirmish game mode in any RTS/RTT. Last but not least, the naval conflicts: it's just too exciting to watch your territories and riches grow and have to formulate quick strategies with your coffers and coal reserves so you can build a solid, fearsome fleet that can outrun the enemy's.
Whether you're playing the main campaigns or the 17th and 18th centuries battles in quick match mode, Cossacks: Art of War shall bring you strategy-ecstasy. The huge battles (details of hundreds of men can be formed), the realistic artillery ballistics, the exciting invasions on the enemy's settlement, the fast-paced management of your resources (wood, gold, food, iron and coal) and workers, and the extreme attention that one has to keep on the keeping up of improvements and specific upgrades, will determine who prevails in the hot war scenario of this game. Cossacks can give you this kind of thrill, if you're fond of the genre.
Bear in mind that, while I'm writing on the Art of War page, this goes for all its "sister" games (European Wars, Back to War).