As I hinted last night, I set my XBox to download it last night while I was working and I played it this morning before going to bed. Here's my first impressions:
It is better called "Left 4 Dead Too" and I agree 100% with you, I thought i was playing more of the same.
I do want to point out a few things. It ran two levels. The downtown and the park. Plus, while you already mentioned that the new special infected are quite similar to the old ones, I must mention that the old ones are still in there. Even the witch, who is now a walking cry bomb (I still crowned her lol).
I'm not too impressed with the new special infected. They don't seem to do that much. The new graphics aren't as gory as I thought they'd be, which is good for me as I do have a limit. I can say the melee weapons were fun. The frying pan had me giggling and I completely neglected my guns while using it.
Overall I can say I enjoyed it. If it's not broke don't fix it. I don't know if I'll be buying it right away though. There's too many other great games on my radar. I'm currently completely obsessed with Borderlands, and I'm geeked for Assassin's Creed II. So while I expect that I will buy Left 4 Dead Too at some point, I don't know when that point is.