Google Groups has been significantly revamped. In true, modern-day Google style, it now looks almost... pretty. It's only the first step of an overhaul, too -- there's more to come, including improved spam control, moderation and search features.
Google has focused on the discussions aspect of Groups first -- so while finding new groups and creating new topics has a shiny new UI, you will have to return to the old interface to perform administrative tasks. Check the New Groups vs. Old Groups page for more info.