I think the Mine Train is a neat little ride, but as the final piece, and apparently the "Center Piece", of this 5 year Fantasyland Expansion it's getting a lot more scrutiny than it would on it's own, and I also think it's taking a lot of heat for the expansion as a whole, because there are few aspects of the New Fantasyland that I take issue with more so than the Mine Train.
I think BOG should have had a better façade, you should enter Beast's Castel itself instead of a big rock/cave with a doll house on top of it. I think Gaston's village probably should have been themed to Tangled instead, with Rapunzel's tower back in that area instead of next door to the Haunted Mansion. And the Circus tent's are clearly just a cop-out, cheap way to save money, but end up being a huge waste of space, they could certainly find a better way to utilize the chunk of real estate.
All that aside, I think of the Mine Train is a step up from Snow White's Scary Adventure, but the location of it seems like a bad idea to me, because of the time and money spent theming the back of it. I think I would have been a better idea to put it where the Circus tents are and had something else in the center of Fantasyland. On it's own merit I think the Mine Train is a nice attraction, but the Fantasyland expansion as a whole is lacking and not really well thought out, but if they got busy designing a decent dark ride where the circus tents are, this expansion of Fantasyland would feel a little more complete to me.