If it's your first tiem playing, it may be hard to get into, but it's worth it. Veterans will feel right at home though.
It's campaign was just the best campaign shooter I have played so far. It changes from a firefight to a battle on a boat. Also, the game really sucks you in with the characters, and you'll begin to feel sad (and happy) to whatever may happen to them. Although there are good things about it, I was kidna dissappointed with the roster. I mean the only "real" new character you got was Tai and...(insert spoiler).
Now, onto the matchmaking. At the beginning of luanch the game's matchmaking was just unplayable. I mean it might of have been left out, and we would have benefitted. Anyways, right now, it works like a charm. I hardly experience anymore lag, and it's always fun and competitive. The only bad parts are:
-Biased Gametypes (Let's face it. You never get to play Warzone. Execution always wins.)
-Hard to get into (For new players)
Now, I will try to describe Horde in 1 word: BRILLIANT. It's just the icing on the cake. It gets really challenging, but it's also very fun with or without a partner.
In the end, I think Gears 2 is definitely a must buy for veterans of the first one, and if you're new to the franchise, I think you should really consider buying it.