It was really helpful as I keep all games and goodies on my disk. I could check what exactly got changed and what I need to download after game on my shelf got updated.

Edit: Please, add changelog to Costume Quest. ^^

Changelog is still there for most games (e.g. for Thimbleweed Park on April 5th). However, among my notifications I also had two games showing up as updated that were missing any changelog information, namely Psychonauts and Costume Quest. No idea what went wrong there.

Ah, you're right, it's missed only in some games. Like Costume Quest you mentioned. :P Thanks.

So anybody knows anything about the change log ? What has actually changed ?

Yesterday a whole bunch of games were updated for better Linux support without updating the changelog.

Pretty much that. You've got all the details from this post onwards.