Don’t worry about it. Sometimes Steam distribution packages are missing essential content, and thus does not allow you to run the program/game. You can go into the client and right click on the name of the game, go to properties and try to verify the contents on your computer with what should have been downloaded. If there are any discrepancies, your client should automatically download what is missing or improper and update the game.
If this still doesn’t work, then assume the latest distribution package has missing pieces, in which case, nobody else can play either.
This happened to me recently, there is a game that showed instant completion of download when I tried to install it. The distribution package was blank/empty.
If this occurs, you can jump on the Steam discussion forums and see how active the developers are and try to get their attention and see if there something they need to do on their end. Hopefully they are active enough to want to fix any problems that arise. But sometimes they are just not around, I have run across a couple of developers who didn’t know that there was an active discussion forum until we dug up their publisher emails and got in touch with them that way.