quoted from my post in the LM forums on this topic:
My own opinion: I feel that the onos in NS right now is just compleatly broken. It costs more than the fade and is less effecive an nearly every situation other than destroying structures. The onos is not a scary and terrifying sight, it is just a big bullet magnet. The change I would make to the onos, would be to impliment damage varients in it's hitboxes, so that the places on the onos skin that appear thick and shielded take half the damage of the fleshy exposed parts. To compensate for the fact that essentially I have just doubled the onos' hit points unless the marines can shoot him from behind, I would decrease his health and armor somewhat until some semblance of balance has been reached. If need be the onos cost could be moved back up to 100 res to purchase if he begins to become too powerful for the relitively easy to reach 75 res cost. In addition, I would replace or tweak charge to the point where the ability is not utterly useless, preferably in such a way that would give the onos a substantial advantage in his basesmashing role.
The armored plating system on the onos would return the onos somewhat to the way he was in 2.0 where everyone liked him. If every marine just focused all thier fire on him like they do now, most of them would probably not do to much damage due to hitting armor; much like in 2.0 except then it was due to the stupid and ugly small hit boxes. The onos would have a higher potential skill platform as there would evolve stratiges to always keep marines on his front side and players would develop a sense for not allowing marines to flank them. In general I think my onos changes could be balanced with only tweaks to the onos himself, and add a wealth of extra depth to the game in thier implimentation.