A brilliant storyline, backed up by old and new characters and gimmicks!
There are many new gimmicks introduced in this game. The weapons which are available no longer have infinite ammo, as you now have to use thermal clips to avoid weapon malfunction. Your weapons can now use many upgrades at the same time, whilst still including the special ammo choices. This special ammo can also be easily changed, as they are now included in the effect wheel. My favourite gimmick, though, has to be the fact that you can import a Mass Effect 1 character, which adds to the continuation.
Overall, Mass Effect 2 is well worth its price. Anyone who liked the first Mass Effect shouldn't miss out on this buy. If you didn't like the first game...why are you even reading this?!