Humble Bundle is an organization that sells games for charity. It started with a service that let users pay pretty much whatever they want for DRM-free titles, and let them choose how much went to the developers, the organization, and the selected charities of the moment. They have branches out since then, sometimes with praise, sometimes with concerned murmors.
Humble Bundle mumble, if you will.
Now they have created a subscription service. Basically, on the first Friday of every month, subscribers will receive the game that is promoted. In other words, it is a service that acts similar to what we're used to, except that you don't know what you're getting ahead of time, you cannot select how much you pay for it, and you cannot choose the proceed distribution. Unless it leads to a unique palette of games that are decidedly better than the typical bundles, I cannot see how this is anything more than a restrictive subset for the sake of it.
Still, that doesn't mean said subset isn't worth your money (be careful of the double-negative). If it is, then you can subscribe now and pick up Legend of Grimrock 2. The title is apparently available on Steam for $24, so this would be a half-price deal if it was something that you were interesting in buying.
I guess that's a decent first impression.