Bush didn't have UN authority to invade Iraq. The Iraq invasion was largely unilateral. There was no clear goal or plan. It was a massive campaign involving land, sea, and air forces. It was theoretically about preemptive self-defense.
The Libya operation has UN authority. It is a multilateral operation (which includes both NATO and the Arab League). It has a relatively clear and simple goal. It is a limited campaign. It's intent is to prevent military forces from slaughtering civilians.
The only way they are similar is if similar means they are complete opposites.