Mass Effect 2 is an action RPG and the second game in a space trilogy by developer BioWare. It continues the story from the first game while streamlining both combat and leveling up. You may choose to import a save file from the first game or create a new one. By importing many of the decisions you made in the first game will have a small impact on the situation in the second.
No longer a Spectre agent working for the alien council, or a commander of a human System Alliance ship, Mass Effect 2 sees Shepard teaming up with the shadowy Cerberus corporation in order to investigate the disappearance of human colonies--and possibly prevent another assault from the Reapers. During your quest you will run into old contacts, as well as recruit new squad members.
Many criticisms of the first game have been addressed. The planet-exploring Mako has been replaced with a faster, nimbler hovercraft called the Hammerhead (while the missions containing the Hammerhead can only be accessed via downloadable content, they are free to anyone who purchased the game new). Secondary missions offer more variety and no longer occur in the same sterile, white-washed facilities that dominated the first game. Infinite ammo has been removed. Weapons now require thermal clips, and sub-machine guns and a variety of heavy weapons have been added to the game. Combat still occurs from a third person over-the-shoulder perspective, but each squad member can now only activate one biotic power at a time--and must wait for it to cooldown before activating another. This speeds up combat by lessening the amount of time spent pausing the game and issuing orders. You still earn points to spend on your squad members by leveling them up, but there are now fewer levels per power and fewer powers available. However, by collecting schematics scattered around the galaxy and researching them on your ship you can acquire new weapons or provide bonuses for your team.
From the game box:
Entire human colonies on many worlds are vanishing. As Commander Shepard, you must assemble the galaxy's deadliest team to save mankind against impossible odds.
They call it a suicide mission.
Prove them wrong.