Medieval II Total War sets your persona in the middle ages shortly before the plague ravages Europe. You can start as one of several factions and begin playing a relatively linear storyline to progress throughout the game. Medieval II is a real-time-strategy game and makes no allusions about not being an RTS however, it does introduce several elements which are typical of the Total War series and not so typical of other RTS style games. The game is mostly played on a world map which shows areas that the player can see and areas he cannot see are covered by a fog of war. Trade routes, city managment, scouting parties, and exploration are major aspects of the game and players who are simply looking for the zerg versus terran style of play will likely be displeased. The game even gives the option of skipping battles altogether and allowing the computer to decide the income, though this is patchy at best and you often lose more units than you should.
Medieval II Total War is not your typical RTS. Units don't have arbitrary attributes so that they may hand to hand one another, instead units are made in large groups of thousands and sent onto the battle field. Rather than units fighting face to face there are bonuses for flanking, charging, cavalry charging, preparing against a charge, and any other sort of battle technique one could think of. The game's AI also plays the different factions quite well. Barbarians are likely to charge you while more sophisticated troops will wait for a charge or move towards you slowly. Overall, Medieval II does work as intended but often gets tedious and boring as later in the game you're tired of missions given to you that don't work with your own goals (often contrary to them) and alliances which are formed never stay formed for long.
Medieval II's biggest issue though is its lake of real time naval combat (present in the new installment of Total War) and its diplomacy system which is yet to be fixed.The issue of diplomacy specifically can cause one to tear their hair out as they try to negotiate a fair deal while the computer beats them senselessly.
Overall I would give the game 3.5 out of 5 stars.