I have a love-hate relationship with Liberty Prime!
As a new, ambitious programmer, I somehow convinced the team that I should re-write Bethesda's pathfinding system for Fallout 3. Navmeshes were all the rage, so of course that's what I started to implement.
Of course, with a large, connected open world, data size was an issue, and I had to come up with a multi-level pathing solution system so that actors could traverse the world even when the player wasn't around. That part of the system was pretty complicated to put together, but it went over fairly well.
What was more of a challenge, unfortunately, was that simple navmesh-based pathfinding doesn't work very well with agents of varying sizes. Navmeshes are very much a precompute-once-use-forever kind of support.
For the most part that wasn't too much of an issue, most characters in Fallout were, if not the same size, in the same order of magnitude! Most actors needed to get through doorways, be they supermutants or dogs.
Liberty-Prime, however, was another story. Tall as a building and as wide as a bus, he broke everything! All the clever tricks I had used until then didn't work. And Liberty prime was crucial to the game, he HAD to walk a pretty long distance while blowing stuff up and throwing nukes and spreading capitalist propaganda.
So I spent several months rewriting portions of the pathfinding system to accommodate him and all the havoc he wrecked. In the process, I made the system able to handle any character size properly, by utilizing a clever 2-pass pathing solution.
And it was all worth it! Liberty prime is awesome! I think one day I'll build a real articulated 12" version of him...