Its been a few months since I've cleared at O'Hare vs Midway. But my memory is "long ass immigration line that is bad for US citizens without Global Entry and terrible for non US citizens" followed by baggage claim and "basically a cursory scan by customs".
The last time I did this I had Global Entry and 5 of the 10ish kiosks were broken so that took a fair bit of time as well (you skip immigration but not customs in that case).
[edit] the time I had a truly miserable experience the line for immigration stretched long down the hallway to the immigration hall. It took more than an hour to see where the citizens vs non-citizens lanes began.