Bachmann's original split frame, pancake-motored designs earned a very poor reputation, and deservedly so. The new standard and Spectrum lines are light years ahead of that old tooling, but it's been a long road getting there, and people are still gun shy (what happened with the Shay has also put people off modern Bachmann, I suppose).
I bought a first generation Spectrum Santa Fe 4-8-4 in the early 90's, and had to send the first one back. The mounting post on the trailing truck just snapped off one day without any abuse. I still have the replacement loco though, and it still runs. The axles never split. But it still can't pull to save its own life... whatever that matte silver plating was that they used on the wheels back then was so slippery that no amount of added weight improves traction much.
When I do rehab older Bachmann steam the first thing to go is that smoke unit. It's just an open cup that makes an awful mess inside the boiler and then dumps its contents when the loco is stored or serviced. I usually shape a lead weight to fill the cavity to balance the weight over the drivers.
As for the newer stuff, there have been problems with things like split gears, but that can be said about most brands, including BLI. I've heard horror stories about BLI steamers being reduced to $500 paperweights because the axle gear split. I've been calling for years for them to follow Rivarossi practice and cut the axle gears out of brass. When you're already charging that much, what's a few more pennies per unit?