I've read a lot of reviews where people complain about how this game is the same as the first one just with a few extras. Isn't that all a sequel is? Differences between Halo: Combat evolved and Halo 2? Slightly better graphics and a couple new guns. You want another example? Look at all the sports games that are put out year after year. What are the differences between madden NFL 9 and 10? Different names on the jerseys and maybe a couple of different stadiums.
I played the first game at a friends house. I wasn't a big fan. Then when I saw this one was coming out, I thought I would try it. I played for about and hour and sent it back. It is exactly the same as the first one. If you liked the first one then you will love this, but I didn't.
I played the first Left 4 Dead for almost 9 months. There are very few games that hold my attention or remain fun to me after playing them for that long, but Left 4 Dead is one of those rare games that really combines skill and team work to make it fun. The versus modes are some of the best out there. There is nothing so satisfying as taking out all 4 survivors or slamming that door shut with all 4 inside. This is one of the best franchises out there right now and if you've never played it you owe it to yourself to pick this game up and at least give it a try.