I went on it twice this past Saturday. It was great fun. We went once in the afternoon and once at night. Slightly different experiences. Daytime was less scary. Night time was a little scarier, but really beautiful. I would love to time it perfectly and ride it at night when Disneyland fireworks are going off.
Unless you are completely terrified of heights, don't let the altitude scare you. It's really quite a smooth ride.
Our Windseeker opened in May and I'm still kind of puzzled how anyone could be STOKED for this ride. I rode it once just to see what it was about, wasn't really that impressed. I had to ride it with a different group of friend just because they wanted to ride it for the first time...
I'm sure it's a much nicer ride at night, but during the day, it really did nothing for me.