A little balance for new GP
First of all, I would like to say that I think Riot has done a great job on new GP. Tweaking a champion to give them a higher skill cap is a great way to change one.
However, giving him an ability that ignores armor, can crit, and does massive AOE damage cost 0 mana is a little bit OP. There should be some mana cost to this ability, especially early levels. Playing against him as a melee top laner is a nightmare early. All he has to do is place a barrel in the middle of the creep wave and then you basically have to sit back and wait for the wave to push to you (god help you if its pushing towards him).