Well first thing first L4D2 was made published by Valve and with Steam client. Also it has no microtransaction. You can have full of fun with it. Most Of Clones are free to play at first but pay to win. Also they dont have strong propaganda as Steam and Valve has. Just check Dota 2 its released and almost beat League of Legends. As popularity. And in cybergame contests. Last tournament give over $16million dolar to the participiants.