The Portuguese are a versatile civilization due to them possessing bonuses in many categories.
The key economic bonus available to the Portuguese is that they gain a Covered Wagon every time they advance in age. This allows for rapid expansion across the map and quick training of Settlers in the mid-game. They also start with one extra settler, although this early-game advantage is extremely brief as they have no home-city settler cards.
The Portuguese explorer has access to the "Spyglass" ability, allowing him to look at anywhere on the map for a few seconds. This makes scouting extremely easy without having to send units into enemy territory. At level 25, the "Bandeirantes" shipment can be unlocked, allowing two more Explorers to be sent to the player. This allows the player to create exceptionally high tanking and killing potential, as on specific maps (e.g. Yukon with its potential curiass of El Pollo Guapo treasure, which gives the explorer 100% health bonus), Explorers can have up to 8,000+ hitpoints each. This also allows for three Crackshots when engaged in a battle.
Militaristically, they have middling close quarters troops, as they are able to train both Hussars and Halberdiers, but their real strength lies at range. They have access to the most powerful Dragoons, and their Musketeers are equal British Redcoats, making them highly capable against hostile cavalry. Enemy infantry can be easily destroyed with Organ Guns; artillery similar to the Falconet but has burst fire rather than one shot projectiles. Cassadors also serve as the Portuguese's Skirmisher, having more damage compared to a regular Skirmisher of their level but has less health, similar to the Strelet.
In other words, the Portuguese army is made up of more specialized units than many other civilizations but, when properly coordinated and micromanaged, they can be extremely difficult to defeat. However, this does mean that they require a degree of subtlety that makes them ill-suited to inexperienced players.
Compared to other civilizations, the Portuguese do not have access to Falconets or Grenadiers, making sieges extremely hard to maintain until the Industrial Age, where Mortars can be unlocked. Their army must also be diverse to maintain effectiveness; an army of only Cassadors and Organ Guns will mean an attack will surely fail, as properly upgraded units like Imperial Czapkas can easily destroy them in seconds due to their high attack.
They do not have any Settler Cards, so the only way to get more settlers is by training them at Town Centers, which can be problematic with low amounts of resources. Although the Covered Wagons can be spread out to avoid being detected, they will be eventually found and destroyed if their economy is still weak. Strategically placed Forts will prove troublesome without Mortars or Monitors to assist in destroying them, as high casualties are expected unless the cannon trick is used - where the attacked unit goes next to the location of the cannons to avoid taking damage from them. They must advance in Age extremely quickly, otherwise their military and economic power will be severely weakened.