Yes I'm a L4D2 "boycotter".
The main issue I see is that Valve keeps vowing up and down that L4D2 is a true sequel but the problem is that it is simply not true. They can say it over and over or scream it from a mountain-top or tell the press it really really is a sequel but that does not make it so no matter how many times they say it.
Quake 2 was a sequel. Half-Life 2 was a sequel. L4D2 will seem so much like L4D that you almost won't be able to tell the difference - they are very very similar in feel, look, playstyle, setting, weapons, and characters. Several tweaks to a few textures and models and then swearing it's a true sequel ("really it is! You'll see you'll see!! Just wait, then you'll see!!) is insane. Well, insane not to realize that all of us can see right through all Valve's positive spin.
Sure it'll probably be a great game because L4D is a great game and they are the same thing with a few tweaks and additions that should have been released for L4D to keep the franchise rolling instead of stopping it DEAD in its tracks like they are now. It's sad really and a shame to see Valve fail to understand some basic principles about gaming in general and sequels specifically. They should know better by now.