Single player is a better experience than the first game. Nice variety of enemies. Level design is better. Replayable.
PRO: Most of the weapons are available early and provide a good variety of choices for combat. New weapons include the Scorcher which is a flamerthrower type weapon useful for hitting enemies in cover and rushing targets. The Gorgon Pistol which is a locust weapon which sprays multiple bullets which makes it effective at close range even when not accurate. The mortar is useful for hitting enemies behind cover, by launching grenades upwards, however challenging to target. Also you can grab a shield and advance using it as cover and firing a pistol at the same time. This is a great idea except it makes you harder to kill, the enemy needs a tactic to counter this, but seems to not have one or not use it. There are several other weapons I could mention but overall there is more variety than Gears of War 1.
PRO: The Graphics have been taken to a new level. I really noticed the difference from the beginning. Greater use of colours. More intricate details. Some enviroments have fantastic backgrounds, especially the underground levels with the water caverns and locust architecture.
PRO: A greater variety of interesting enemies. Some of the encounters will have you facing a small horde of locust enemies. Some of the new types of Locusts include a giant gladiator carrying a shield and wielding a swinging weapon. There are also some beast riding varieties. These new enemies really highlight the locusts as montrous opponents.
PRO AND CON: Great developing story, which is really setting up for a sequel. The ominous mystery surrounding the plot actually helps the game. The only CON with this is that new characters seem to be not used to any great potential within the story which is disappointing.
CON: On the lowest differculty this game is quiet easy to progress. Definitely easier than the original game. This is probably due to your squad mates having lots of health and not dying. They will also do their fair share of killing the enemy. On many encounters the squad stomps the opposition. This is actually a good thing though, but I recommend setting this game to higher differculty levels. The boss encounters are easy and are thus disappointing.
Overall a fun game, with some decent replay value, more so than the original.