Does it make a difference if I play through L4D1 in L4D2 or in the original L4D1 game
 

Me and 2 friends are playing through the L4D campaigns fresh, we actually did L4D2 campaigns first, and now we're moving on to L4D1. Originally I just planned for us to do the L4D campaigns on L4D2 because I didn't think there was any difference but I came across a comment on this subreddit mentioning Dead Air's forced crescendo at the metal detectors in L4D2 making it harder, which I don't mind, but another person replied to it with a comment saying, "There's something very off in L4D2's version (of the original maps)". I couldn't find any detailed info on that and since the original game is $10 with no sale in sight and I'd have to gift it to 2 people, I wanna be sure about this lol.

Do you guys think it makes a noticeable difference playing without 2's special infected/weapons/different HUD, etc.? Are the zombies in general placed differently? Is the vibe/ambience different?

Re: Does it make a difference if I play through L4D1 in L4D2 or in the original L4D1
 

Both games has some differences, you can find some stuff here:
https://forums.alliedmods.net/showthread.php?t=339533

Basically, L4D1 has a darker atmosphere while L4D2 has brighter maps and textures.
Also, L4D1 has a specific map (map*_vs_*) for versus and for coop, while in L4D2 they just one.
Some maps have different paths and models because of a balance perspective, since L4D2 brought some new SI, weapons, etc. (like No Mercy finale is open air in L4D2 and L4D1 has walls on the second floor, radio area)

L4D1 doesn't have melees so IMO is harder, causa melees are overpowered in L4D2

Re: Does it make a difference if I play through L4D1 in L4D2 or in the original L4D1
 

If you want to play original horrible game (no melee, no powerful weapons) => play l4d1 maps in l4d1
If you still want to play fun with friends => play l4d1 maps in l4d2