The only way to play L4D is with friends.Yep, that's how L4D . Every single time. At least you didn't get team killed the second you entered the game. Worst, most hostile online community I have ever seen, truly abysmal. Absolutely not worth it if you aren't playing with friends only.
Played some Batman: AA and it seems even better than AC and I loved Arkham City to the point where I got 100% on it on PS3
AA is a much tighter, more streamlined game. AC had what felt like a larger world, but it also suffered due to this.