OK, here's my thoughts. It's taken me a while to write them up. First, the Timberliners:
I didn't like them. I hadn't ridden Hades with the old trains, but it felt very VERY bumpy. The bottom of the first drop was awful, and the restraints tightened from the bouncing to the point of being painful. The seats themselves are comfortable enough, but the steel wheels are really rough. Like I said, to the point of them being unpleasant. Now to give them the benefit of the doubt, I had heard bad things about Hades before, but I was hoping that the new trains would at least be some improvement. It will be interesting to see how they ride on The Voyage, but I'm not hopeful.
So now onto the inversion:
I'll give them one thing - it looks pretty great. Anyone that's been to Mt Olympus will know that the drive into the park wraps right around the trojan horse, and around the part of Hades that pops into the parking lot. It looks brilliant - with a great twisted mess of track of supports.
As for on ride (ignoring the train problems I spoke about above), the inversion is a lot of fun. You come flying out of the tunnel and straight into the inversion. It's fast, it's smooth, it's noticeable, it's fun. After the inversion there's an overbanked turn, before heading back into the tunnel. Overall the upgrade is good, but Hades is still a rough ride and I don't know how much the Timberliners have done for that - be it good or bad.