I finally got to ride Manta today and I have to say I was very impressed. The layout is great because it gives great visuals of guests all over Sea World, it has perfect B&M smoothness, and the ending is great with the low to the ground dives and close (sometimes too close) dives to the water. I was only able to manage 2 rides one in the middle and one in the very back. The queue line is cool, dark and provides plenty of entertainment while waiting. They even have a great soundtrack playing while waiting.
As far as a comparison to the other flyers, I've been on both SFOG and SFGAd Superman rides and Tatsu - I think it's clearly a big step up from the Supermen ride and I honestly prefer it to Tatsu. I can see where a lot will like Tatsu better, but I think Manta gave an overall better mix of sensations than Tatsu and Tatsu seemed to just power it's way through the whole course (which is a good thing too). Manta had several intense moments, but some nice fast, gliding-type moments too which is when flyers are their best IMO. The pretzel on Manta was intense enough, maybe not quite as intense as Tatsu, but very close. However, I loved the sequence after the pretzel which was a roll over then an intensifying 270 degree spiral dive that went back, threaded the pretzel and did a corkscrew type element into the block brake. The ending was not very intense, but the interactions with the themeing, water and ground more than make up for it. In fact, the back seat gives a really nice sensation when you dive out of the block, something kind of unusal for a flyer.
The length is fine and pretty much perfect. It's a rather quick (and deceptively high) climb to the top of the lift and you get great views of people walking below. The dive off the lift gives a great whip in the back row.
Overall, I'm really excited about Manta and can't wait to go back and ride some more. Honestly, when it was first announced, I didn't know what to think because I've never been a big fan of flyers, but I think it's going to be a hit. I loved it and the public seemed to LOVE it too. I'm sure I'm leaving some good points out.