The main problems I have with L4D2 are two things:
1) Broken Promises
2) Price
1.
http://www.videogamer.com/xbox360/left_4 _dead/news/valve_details_post_left_4_dea d_launch_plans.html
The Valve CEO has stated ( "we will" ) that there will be more content for L4D1, for free. Namely, new campaigns, new characters, new weapons, new unlockables, new achievements.
So basicly Gabe said we should've gotten the following:
10 or more new Maps ( since a campaign is 5 maps )
2 or more new Characters
2 or more new Weapons
2 or more new Unlockables
2 or more new Achievements
What we got:
1 new Map
0 new Characters
0 new Weapons
0 new Unlockables
Plenty new Achievements
1 New mode
So the only thing they kept their promise on it new achievements.
As a company, it's not a very smart thing to promise things and not to make them true. After the release of L4D they immidietly began development on the new content. They made new weapons, new campaigns. But durning that development, they thought, why would we give this for free? We don't owe them anything. They either simply forgot or ignored their past promises there.
I do realize that they might still update L4D, but why would they update an old game that already has a sequel? Valve has also stated somewhere suddenly that they "Might" do things instead of "Will". Haven't got the quote on this but it was on one of the many interviews. Read through them if you want.
Not only broken promises, but also trust. They sold us L4D under the impression and advertisement that it would get regular content updates. They would sell the product as a "service". Knowing Valve's earlier products such as TF2, people entrusted Valve with a full price for a low-content product. Everyone expected content updates, since another game got them too that isn't even half of L4D's price ( TF2 ), but instead things turned around and the free content turned into a full priced sequel. Not only will this cost the user but also split the community between two standalone games.
2.
Price is also a big factor. L4D2 seems to be going superior in every way content and gameplay wise. It has all the things L4D has and more, including all the improvements to the networking code and AI. This is a big letdown to the people who bought the first product at the full price. Not only did they expect a product recieving regular updates as Gabe told, but also a product with a long lifetime. L4D2 basicly means that little people will buy L4D1, as that product is inferior to the second installment. Which could result that L4D1 will slowly lose players.
With L4D2 being basicly an improved version of L4D1 with more content and another setting, one would expect it to be an expansion, or downloadable extras. Making it a sequel this early only angers people who bought L4D1 at the full price. They could've gotten a better product in such a short timescale. With such similarities and only improvements, a low price expansion would be expected, not a fullprice sequel.
What should Valve do?
A. Make L4D2 a 20-30$ expansion, this would obviously be the best solution. Not only would an expansion allow L4D and L4D2 be compatible with each other, give current customers a fair deal, but it would also allow Valve to update the game with the "Free Content" they promised for both L4D and L4D2 at the same time.
B. Introduce L4D2 to current L4D owners for a discounted price, 10-20$ would be a fair price considering the extras, minus all the promised free content.
C. Cancel L4D2 and change it to the free content as promised. Considering they already announced L4D2 this would obviously be the worst solution for Valve, but the most fair solution for their customers. It would obviously not work.
In short:
L4D owners were promised free content, instead of getting the free content they put it in L4D2 and announced that. People are angry because Valve broken it's promises and offers them to purchase the supposed to be free updates for a full price. The introduction of L4D2 will cause the communities to split meaning less players to play against. This has only shown that Valve is starting to prefer quick money over trust and reputation.
PS: L4D is not made by Valve's main team, but by Valve South, also known as Turtle Rock. They were the ones who made Condition Zero ( which was an absolute failure ), that may explain the whole thing. This still doesn't make the fact right that Valve's CEO announced free content updates.