The Ottomans are an artillery based civilization, with most of their units being considered as such.
Ottoman artillery, along with the British and Russians, can be built at the Colonial Age, rather than the Fortress Age. This allows them to have a very strong anti-building and infantry force. Many of the Ottoman units are equal to other units, mainly compressed into that type of unit.
The Abus Gun is a powerful light anti-infantry unit which can deal massive damage against infantry. Since their attacks are classified as siege rather than ranged, they also ignore the high ranged resistance of other artillery, they are just as good at taking them out. The Ottomans only have one infantry; the Janissary, which is comparable to the Musketeer. They also have fairly decent cavalry options. Their Grenadiers and Hussars also have the Royal Guard status. The Great Bombard is a powerful artillery piece which deals massive damage to anything it hits, being a mix of the Falconet and Mortar. They also have the Spahi, a unique Ottoman heavy cavalry unit which is capable of regenerating health. Spahi automatically upgrade whenever the player advances in Age.
Economically the Ottomans have the advantage of being able to spawn settlers at no cost. This limit can be increased with Mosque upgrades. Players are initially limited to 25 settlers, but increases to 45, 70 and 99 respectively. The train time can also be decreased significantly from the Mosque upgrades - essentially, as long as an Ottoman player still has their Town Hall or can construct one, they can still have a fighting chance.
The Ottomans have unique church upgrades; however, it only sends military units - 12 Janissaries and 3 Great Bombards.
At level 25, the Ottomans can send the "Battlefield Construction" card, which allows Janissaries to build Barracks, Stables and Artillery Foundries. This can be used when starting or prolonging a siege at an enemy base, as there isn't any need to divert settlers to create a forward base of operations, and players can use military buildings at their colony for defense.
The Ottomans are very artillery-intense, and thus many of their units will cost a substantial amount of coin. Due to this artillery-intense composition, the Ottomans have essentially no infantry or cavalry options, and since artillery is weak to cavalry, players must use Janissaries, Hussars and/or Cavalry Archers in order to protect them.
Essentially, any player who is able to muster powerful cavalry can easily wipe the Ottoman's military strength, as the Janissaries can be taken out with ease with protected artillery. Such examples include the Germans, who can use Falconets to pick off the Janissaries while the Uhlans stampede through their artillery.
Players playing in post-match Industrial/Imperial Ages must also kill off settlers periodically from their Town Centers because they will keep producing settlers, which can hamper an army's composition.