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. For example, the Abus Gun is a light artillery piece that acts as a Skirmisher. As Ottoman units are mainly based around artillery (they have 6 artillery units, the Abus Gun, Grenadier, Falconet, Culverin, Mortar and Great Bombard), this makes them susceptible to cavalry units. To compensate for this weakness, the Ottomans have the Janissary; the Ottoman's version of the Musketeer, and the Cavalry Archer. The Ottomans also have a decent cavalry force, as their Hussars can be upgraded to the Royal Guard status. They also have the Spahi, a unique Ottoman unit which does area-of-effect damage. Great Bombards are a mix of Falconets and Mortars; they deal a whopping 750+ damage when properly upgraded, easily killing most units while dealing massive damage to buildings.
Economically the Ottomans have the advantage of being able to spawn villagers at no cost. At the start of the game settlers will start spawning for free up to a certain limit, which can be improved through upgrades found at the Mosque.
The Ottomans have some decent unique church upgrades, although the focus more on military than their economy. Their two corps techs sends 12 Janissaries and 3 Great Bombards respectively, allowing for a firepower boost when launching a siege.
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, troops can be sent to prolong the siege, as if the opponent is too far away from the player they may have time to restore its defences when the player's next army attacks. Essentially, it acts as a mobile fort when all three are constructed and there are troops stationed there.
The Ottomans lack the variety of units the other civilizations have, as the Janissary is their only infantry unit. They only have three cavalry units: the Hussar, the Cavalry Archer and the Spahi. Considering that the Spahi can only be sent through the Home City, this reduces them to Hussars and Cavalry Archers if no more Spahis can be sent. Most of their units consist of artillery, and are vulnerable to Culverins.