I went through some of my assembly backlog recently, and the War Crow A and Prey Seeker were super easy to assemble. They looked great when completed as well. I also did another Ursus II, and ran into the same problem with that sculpt that I had the first time I did one: I have a tough time getting the right arm into a position where it doesn't interfere with the 'flap' attached to the back of the mech. The left arm is fine, it's just the right that causes trouble, and I usually end up cutting/filing a significant amount of metal off before I get them to both line up nicely.
I also put together a Leviathan I picked up at either Origins or GenCon at least a year ago. It didn't feel like it was up to the usual IWM standards. The attachment points for the engine nozzles were vague and not aligned all that well with each other. I got them all on, but getting them oriented so at least one of the four didn't look wonky wasn't happening. The fact that the engine nozzles are oval instead of round made it even harder to get them all to line up and look of-a-piece. The arrays of tubes that mount towards the front of the ship were OK, but again the mounting point for them was very vague on the main body of the ship and it took some adjustment to get them both to mirrior each other in position and angle. The detail on the main body was a little fuzzy in general, but that is as much the fault of the source art as anything IWM did. Lastly, there was no way in heck the included post was going to hold the mini up with just superglue or simple pining. The ship is too heavy and the attachment points are too small. I ended up throwing the included post away, drilling a hole through the included base, drilling a hole about 1/4" deep into the belly of the mini its self, and using a ground down roofing nail going through the base and up into the mini to support it. The Leviathan could use a re-think on the attachment points on the body, and the way it mounts to the included base.