To be clear, it's just the frontend for now. Frontend as in the client-side stuff and the backend stuff required to directly support it. The core backend code that manages the games and what-not is not currently available, though it looks like that might happen eventually.[1]
OGS (online-go.com) is great.
I am impressed that it hasn't taken over KGS by now, which is to my knowledge the largest western server.
I have tried Pandanet IGS, KGS, Tygem, WBaduk and even obscure ones such as Fly or Die and Go Chat (Facebook messenger bot).
I think OGS offers by far the most frictionless way to start and a more modern UI. It even offers really nice features such as the ability to draw on a board during a review.
I just wish it had a plugin for something like BW Go (Android). A decent offline client with manual sync, exploration, perhaps conditional moves. There is a plugin for Dragon Go Server and it's so much better than dealing with mobile browsers.
Do all of these servers not implement a standard protocol? I've had similar frustration with OGS on mobile, and at one point I toyed with the idea of learning iOS by building a Go client that worked with all of these servers.
One of the developers of OGS here! We're pretty excited to make this happen and continue development of the site and hopefully bring Go (the game) to a larger audience.
All that said, I'm glad to see this happen!
[1] https://forums.online-go.com/t/the-online-go-com-user-interf...