Invisible, silent and subtle, the infiltrator class packs all his punch into one clean shot. Perfect for people who would rather take their time and some pride in their work.
The Infiltrator's power comes from its ability to thin things out from a distance as well as up close.
The sniper rifle provides a well placed single blow that can take out the most cumbersome foes. When using the scope, time slows down allowing an easier time targeting geth. In addition, the invisibility cloak keeps your enemies off your back in order to secure a well placed shot.
Infiltrator's can also use their tech abilities to hack ai. This creates a shield around a hacked target, who then considers you an ally. Not only do you add an extra man to your side, but it takes a few eyes off you.
The Infiltrator's path comes to a head when pursuing either the commando specialty class or operative specialty class. The commando is a soldier with a plan. They deliver well placed methodical shots to dispose of their enemies. The operative specialty class manipulates the environment to your advantage, with faster ai hacking and further development of the sabotage and overlord abilities.
In the words of the immortal Llavar Burton, you don't need to take my word for it. Replaying through ME and ME2 is a blast, pick up the infiltrator and I can guarantee that you will be using the class when you start up ME3.