There's a few reasons people around here dislike the MP. First, they displaced the F40C, a legacy MILW locomotive from the seventies. Even though it's and SD40 with a cowl body and HEP generator, it was a rare permutation and people dig that like they dig Alcos. Second, it's a crummy design - Metra demanded a locomotive powered by the long-out of production 645 block, and they got an MP36. EMD doesn't want anything to do with building 645-powered engines. It's also quite heavy. I'm not sure why it's so much longer than an F40PH, but it's 30% longer (not fact-visual estimation, no flaming please), so it's obvious where the weight comes from. They also have had numerous reliability issues, as passenger locomotives aren't build in as large of numbers as freighters they don't have quite the R&D budget.
The poor design, reliability, and displacement of legacy locomotives is a "three strikes and you're out" in the mind of a railfan, espcially one that has no direct financial connection to the performace of the railroad.
I personally have nothing against them, although they aren't my favorite. I'm a classic F40PH and F40PH-2 man, myself. If I had my endless railfan dream, the M's, C's, and MP's would be working in some other place like Montreal or LA, and the Rock Island, BNSF, and CNW lines would be electrified at 1500DC like Metra electric and South Shore. But let's be real, that's never going to happen.
The new Acela: It's not Aveliable.