It's basically a commercial-multi w/ instrument privileges. The performance standards are slightly tighter than commercial, but that's about it. Look at the PTS.

The oral could be very unpredictable depending on whether you do the 121 or 135 version, abd depending on the examiner's background. Best to do this one with an examiner you know.

You can remove some of the variables by doing it at one of the pilot factories like ATP, but you might be in unfamiliar airspace...obviously your local airspace provides a home-field advantage.