I think it's doing well. I've been paying for it since June and I haven't looked back. For me, it's been either equivalent or better than Google for work-related (programming) searches.
Getting better, definitely. I've been using it since beta, and while in the early days I'd use !g often to switch to Google, it's been months since doing that has made a difference. These days, if Kagi can't find it, Google can't either.