Civilisation 5's tech tree vexes me.

[factotum]

It's a good idea but I wonder if in practise it would fall down because it is either A) random (and that can ruin games)

There is already a fairly significant random factor in Civ games--the location you start can make a huge difference to your early growth, which can have knock-on effects throughout the game. Adding another random factor wouldn't necessarily make much of a difference, then, IMHO.