Diablo 3 requires a constant connection to the internet to be played. Get disconnected, and the game will drop back to the title screen and remain unplayable until it can connect again. So don't plan to take Diablo III with you on long flights or anywhere else you won't have access to the Net. The move doesn't come as much surprise as developer Blizzard Entertainment took the same approach with Starcraft 2. Nevertheless, for a game many people play solo, and potentially on their laptops in all manner of on-the-go situations, Diablo 3's connection requirement poses some potentially frustrating limitations.
Blizzard's Rob Pardo explained that Diablo 3 requires a constant connection because all characters are stored on Blizzard's Battle.net servers. This setup allows Blizzard to authenticate all characters and items, adding of protection against player fraud and duplication of items. This latter point becomes particularly important with the (just announced) advent of real money auctions for items in Diablo III.
Pardo went into some additional details about the Battle.net improvements planned for Diablo 3. Finding friends and getting together with them to play received the most attention. Diablo 3 incorporates cross game chat, allowing players to talk with their friends playing Starcraft 2 and World of Warcraft. It also ushers in a new persistent party system for keeping groups together.
It will be easy to hop into games with your friends using a quick join function, and Diablo 3 supports dynamic co-op, allowing people to come and go. To help with matching players up compatible partners, Diablo III has a new banner system. The banners will change to reflect a player's accomplishments. So before jumping in to join someone you'll know what you're getting in to. They also serve the handy function of teleporting anyone who joins a game in progress directly to the banner holder. No longer will you have to immediately ask for a town portal.
Many of these new Battle.Net features will be available during the beta test which is expected to begin soon. For more on the what to expect when it arrives, see our Diablo III hands-on preview.