This is not a complete web player à la Spotify. You can not browse the catalog, create playlists or see what your friends are playing. There is no guarantee that you will see a dedicated web client in the future. However, it is still miles above the previous functionality, and suggests that Apple is taking web reproduction seriously where it used to be a marketing tool for the company's native music applications. Do not be surprised if Apple says about this at WWDC.
Somehow, Apple may not have had many options. If you're going to catch up with Spotify, that means offering players anywhere Spotify is an option, and that includes the web. You are more likely to subscribe if your favorite review site can include the version of an Apple Music album instead of the alternative services. This also helps Apple to offer some kind of service on devices where the installation of an application simply is not possible, such as a locked work PC or a Chromebook.