There is no new web store, and nothing has changed about GameStop.com, except that you can now see a "Buy Digital" option when looking at their PC games. This option has been around for a while on some games, but now GameStop wants to expand its efforts. For example, there is their attention-grabbing sale on digital copies of Left 4 Dead 2, now only $10. You can still choose to order the traditional copy of the game in a box (which is currently $19.99). Free trials of certain games are also available.
It will be interesting to see if these sales continue, and how the digital sale of PC titles by one of the largest purveyors of video games will affect the market. GameStop's sales could spur many reluctant buyers to take advantage of the savings on the digital copy, and this could have the potential to make more customers receptive to buying digital. GameStop's online store may make digital distribution more visible to people who had not encountered it before. Not all buyers of video games are aware of online stores like Steam (there's the stereotype of clueless parents who buy whatever brick-and-mortar retail stores tell them their kids will like), but just about everyone in the United States has seen a GameStop store or been to their website. This could demonstrate the ease (and savings) of purchasing PC games online to many people who had previously been unaware of the option.
It's not surprising that GameStop has the means to open an instantly-competitive digital store. After all, they are the game store that consistently gets great pre-order bonuses from publishers. Of recent note on this subject, GameStop reliably distributed Fallout: New Vegas pre-orders, and BestBuy did not, canceling many pre-orders due to a shortage of stock, and leaving a wake of angry customers. GameStop is also associated with Barnes and Noble, one of the leaders of digital book distribution, and handles their video game sales.
This page on GameStop's site gives all the details of their new store. According to the graphic on top, Xbox 360 games will be coming soon. If you are considering ordering digitally and want to compare GameStop to competitors, take note of the following from their FAQ:
Can I install the product on more than one PC? This varies by publisher and product. Some products can be installed on only one PC while others can be installed on up to three PCs. Your email receipt will display the number of licenses available.
Compare this to Steam's ability to download and install games an unlimited number of times. However, GameStop's FAQ also says that games lost due to a PC failure can be recovered, so perhaps there are options for that. Additionally, GameStop gift cards cannot be used at this time, because digital distribution is handled by a third party.
Who is the "third party" that handles their distribution? I haven't turned up an answer yet. If you know, please leave a comment or write email@example.com. And if you have any stories of your experience with buying digitally from GameStop, I'd also like to hear about that.