[Update:It seems that Jurassic Park: The Game and all previous seasons of The Walking Dead have been removed from Steam. You will still retain access if you've already purchased them.]
According to a report from GameDaily, Telltale Games is now entering the liquidation phase of its closing process. This is coming after September's shock announcement that the studio had laid off a majority of its staff and kept around 25 employees to finish off contractual obligations to other companies. It still seems like yesterday that we were first hearing about this.
While most people don't really care to hear all the business mumbo-jumbo behind this process, the immediate effect for customers is that some games have been delisted from Steam. Currently, you will no longer be able to buy Back to the Future: The Game or Tales of Monkey Island from Valve's digital storefront. As of the time of writing, both games are still available on GOG.com.
This is likely more to do with licensing issues for both titles instead of the liquidation process, but the titles are likely to disappear from other storefronts in the near future. If you have been eying picking up either game on PS3 or PC, make sure to do it now before they completely disappear.
If you are more interested in learning about the business behind these decisions, GameDaily's report goes into pretty extreme detail about who is handling the liquidation and what it will mean for the current employees of the company. Since I'm not so up to speed on business jargon, it loses me in the middle, but it seems that Telltale will be closing a lot sooner than expected.