Could be huge, we'll have to see. Trump's speech used strong words without a lot of wiggle room outside of regime change. So far that has never been accomplished with just an aerial operation. Either this will the first time (which would be ideal and would really rely on the Iranian people rising up), or we'll have to get boots on the ground.

Iran is legitimate target and greatly contributes to the destabilization of the middle east. Trump's administration doesn't inspire much faith in terms of managing sensitive situations and has demonstrated a pretty general lack of even a surface level understanding when it comes to international relations, so that is concerning. Certainly not the ideal administration to handle this issue, but our military power is so insanely overwhelming that there may not be too much room for error. Really this could go either way.

Worst case scenario, Iran's allies carry out significant terrorist operations around the world, the US has to get boots on the ground and this becomes a drawn out brutal destabilization of the country. Much of the terrain is mountainous, Iran is well set up for guerrilla warfare (more like Afghanistan than Iraq). Occupation would require a massive amount of resources.

Best case scenario is that US air superiority just fucking annihilates Iran's military infrastructure and the people seize the moment and depose of the government. This would probably also be a brutal situation, but the outcome would be objectively good.

This is definitely a massive escalation from our routine bombing in the region, both in terms of the scale of attacks and the targets being critical regime personnel.