Change Zilean's Sticky Targetting
Please have the bombs prioritize bombs that are already placed, regardless of how close other targets are, or simply have it so that the bomb - stun goes off when their reticules touch.
Also I don't think it would break him to increase either the sticky radius or the travel speed. It's currently way to easy to avoid them. The onus on targeting is much too heavily on the zilean, given the massive mana costs.