Well, I rode Hydra opening day, and then went back last Friday and rode it again.. it's getting better!
To really ride it you have to do it at night, after the track cools a bit, and be in the back seat. I actually felt some positive and negative G's on friday night about 9:15... but the front seat, while good for the "track gon' eat my feets" illusion, is lousy for the ride.. with a bit of headbanging as it gets yanked around by the back of the train. The back is pretty smooth, and while, as noticed above, a bit clanky and rattly, it still moves smartly along.
The only major complaint I have is theres one station.. and it is only large enough for one train. On friday they had a charf hold.. (someone charfed in their seat as it was coming into the station) and they let it sit for 20 minutes in the station for the de-charfing stuff to work. Meanwhile, the second train sat on the transfer track, with the folks swinging their feet and no means to get off the sucker.
I'm by no means a B&M expert, so that may just be the way they are designed totally now, but it seems like lousy engineering to me, that if they have to change a wheel or something, the second train is just hung out to dry, full of people, like that.
But all in all, a good addition to the park.. tho Talon is still "it" for me, in that particular park.
Maeryk