The most important decision you will make in Mass Effect 2 isn't a choice of who to save or who to leave behind. In fact, it is the class that you pick at the start of your adventure, and there are quite a few to choose from (each is much more interesting than its counterpart in the original). Below is the low-down on each class, and tips on playing as them.
The Soldier is a great class for newcomers to the series and experts alike, and it is a lot of fun to play as. Obviously this class specialises in the more traditional weaponry, such as assault rifles, grenade launchers, and sniper rifles. This allows the player to equip special ammunition, such as incendiary or cryogenic bullets, that perform admirably against certain enemies. While lacking biotic skills, Soldiers can deal with shields using their Disruptor ammunition. Another notable skill is Adernaline Rush, which slows time and allows precise aiming.
The Adept class employs biotic powers over weaponry (though they can use Pistols and SMGs). There are a variety of fantastically satisfying attacks that they can perform, including Pull and Throw (think Jedi and Stormtroopers) and Shockwave – each of these is brilliant at lobbing enemies across the map. Some can be immune to such action, if they have a shield or barrier for example, though the Adept's Warp ability is good against barriers and armour.
A good assistant to a squad of any other classes, Engineers can make use of high-tech gadgetry to help out their allies. With the same default weaponry as the other less combative classes (Pistols and SMGs), their trump card comes in the Combat Drones that they can bring to the battlefield. These cause sporadic damage to shields, while drawing enemy fire. Engineers can also cause great damage with attacks like Incinerate and Cryo Blast, while Overload will rip through an enemy's shielding, making an Engineer a clever addition to a biotic squad. The addition of the AI Hacking ability also allows them to wreak havoc among enemy robots.
The stealth class in Mass Effect 2, the Infiltrator has the Tactical Cloak power which allows them to disappear and avoid enemy detection. They also have the benefit of being able to use Sniper Rifles as well as the default weaponry. One of the most intriguing powers in the game is the AI Hacking ability. This is also available for Engineers, and allows you to hack into an enemy drone and send it to attack its former allies! Infiltrators can also use Cryo Ammo as well as Disruptor Ammo, allowing them to take down enemy shields.
The Vanguard class attempts to strike a balance between the Soldier and Adept classes. It can use a Shotgun in addition to the default weaponry, and sports certain biotic powers to help disable enemies and allow the player to get close-up for the lethal shot. Cryo and Incendiary ammunition increases bullet damage, while Shockwave and Pull come out of the Adept's armoury. Both of these attacks can slow targets down and allow close-quarters kills. The Vanguard class also has the fantastic Charge ability, where the player uses their biotic abilities to thrust across the room towards a target, knocking them down and setting up the killing blow from a shotgun. Unlike most biotic attacks, Charge works through obstacles as the player shifts in and out of them.
Sentinels are a balancing act between the Adept and Engineer classes. They have high armour, allowing them to inflict damage and assist their squad throughout a battle, even under intense fire. They are particularly weak in terms of weaponry, but combine the shield-destroying Overload of an Engineer (and Armour destroying Warp) with the bone-crushing Throw of the biotic Adept class. With the Tech Armour ability, shields are increased and if they happen to be lowered, a shockwave is sent out, damaging nearby opponents. They also have the Cryo Blast attack available to unlock, freezing enemies where they stand.