It just took exactly the direction I did not want it to take. Emphasis on combat over exploration, dumb, padded out, waste of time puzzles, identical patterns for nearly every boss fight (shoot back the huge orb! jump over the shockwave! pull off the cover to hit the weak spot!) to the point where it felt like a tech demo. It was so linear and straightforward (go here! says the poor voice actor), celebrated for all the reasons I disliked it. Sure, that sky town place looked great... but it was literally just a series of monorails that shuffled you forward. There was like, what, one power up that was not directly in your path? Maybe two? And then there was the page out of Sonic's handbook with the introduction of Samus' shitty friends. The whole thing felt like a huge step back.
I liked the abandoned ship and the Metroid facility. And Ridley's appearances. I disliked everything else.
It wasn't at all what I wanted. Prime 2 was so great. Difficult, with sprawling areas, a little plodding early on but with huge payoffs in the form of challenging, thoughtful boss fights. Prime 3 was such a regression. I wanted to like it, tried to, couldn't.
I did like DKCR. That renewed my faith in Retro's direction. I'm hopeful about their future games, but I can't enjoy MP3.