Some think that L4D is mostly a ripoff to Resident Evil: Outbreak Files 1 and 2. I can give you the sites if you want.
Not trying to go into full details of everything, but hopefully this will all clear everything up. I said I felt L4D was a ripoff in some of the elements to RE. One thing, well it's just how I see them ( maybe not for anyone else ) is that I think Zoey and Claire look really similar and some of their bios about them is similar ( One of them being they both are University Students ). Resident Evil clearly expresses that Tyrants and Lickers were regular zombies at one point, but evolution took hold so to speak, so that is why I mainly compared those two to the zombies in L4D. I think that the Lickers, Hunters, Tyrants and Hunters in RE and the Hunters, Smokers, and Tanks in L4D do the same basic thing and mirror each other which is why I continued to say I think L4D is a ripoff on those elements.
Quick recap:
Hunters from L4D and Hunters from RE: They both jump and pounce and scream when you are near them. Difference: The Hunters on L4D are humanoids whereas The Hunters on RE never derived from a human.
Lickers vs. Smokers: As you said, they both attack with their tongues, but they both came from humans. The difference: Smokers like most bosses in L4D explode.
Tyrants ( Nemesis included ) vs. Tanks: They both are capable of doing swings that will knock the character down, ram into them, or send them flying. Difference: Tyrants may proceed to jump on you, may kill you in one swing, and can bash through walls. Not sure if that happens on L4D or L4D2, but correct me if I am wrong.
I also felt it was a coincidence that Their states regions are near each other, meaning that if RE wanted to spread out towards Pennsylvania, it could in a matter of days. Say for example, I live in Texas and Alabama is far away to someone else if they think it is, only their regions are seperate. I think of it only as being a couple of states away, so that's how I felt with that, lol. Now apply that to RE and L4D and it will reach Alabama in a few days whereas if it was from Texas to New York, then I could say a week or so. Why did I compare the two with regions: Because as I said, I feel they are both close even though Raccoon City is fictional, but in the MidWestern region whereas Pennsylvania is real and is in the Northeastern region. Both regions are close to each other.
I also felt the way the outbreak took fast was rather odd as well. Motel said that with 28 Days/Weeks Later it happened fast as well and I have seen it, but I think that RE and L4D had the exact same thing of how fast the outbreak went, which is why that was another reason why I said that was another ripoff to RE.
I haven't played the game, so that was one thing you all have against me on that, lol.