Just finished it in a two and a half hour game. Dani dropped about two hours in... sorry dude!
Rail ride section was cake for us. Took us maybe five or six tries. The biggest problem was that we couldn't checkpoint prior to the ride, so every time we died during the rail ride, we restarted back with the Drones and Hunters (and everything else) still alive. Eventually we got a checkpoint though.
For the rail ride part, the grenadiers just have to learn where the Shade turrets are and blast 'em right away. Like I said it only took us five or six tries.
Spire section took a while but not too long. Nightshade snagged a Banshee, and Hayes and I lured the enemies outside and Nightshade knocked them off the tower.
The hardest area was probably the oil rig facility or whatever it is. We just couldn't figure out a good way to tackle it, even using the catwalks. There was probably a much easier way to do it than we did.
Overall, it was a blast. One of the most fun campaign sessions I've played in a while.