I am not going into any more detail since I don't want to spoil the story, suffice it to say, it is epic. The action is on a much grander scale then its predecessor, making you feel like you're right at the heart of this war. There are some emotional moments in the campaign as well which gives the characters a little more depth. But most importantly it remains fun all the way through.
The multiplayer is an absolute joy, with many of the early bugs now ironed out. The matchmaking system means you no longer get kicked from games for no apparent reason. The new gameplay techniques such as wall mines and boomshields make the multiplayer even more frenetic and addictive. The addition of chainsaw duels also makes for some tense standoffs, and once each team is down to one player each a 60 second timer appears. A relief for those who have been kille and are watching two people attempt a headshot 50 times over.
In closing, this really is a game that should be in your collection. The campaign is epic and the multiplayer will keep you playing until Gears of War 3.