It has been a challenging experience.
I've edited several short stories for publication in the recent past, namely my erotic romances for Total-E-Bound: Captive Angel and Country Hearts.
Perhaps because they were for far shorter works, those edits were relatively easy. Yes, I had to change fairly major aspects of the pieces, such as tweaking the death of a character or changing a sex scene, but these were discrete scenes that required specific thought, not a major overhaul.
These latest edits were major overhauls. I was tasked with revisiting the pasts of the characters, questioning the heroine's characterization, and changing an overly sweet ending. I struggled with the edits for the entire two weeks I had to rework the manuscript.
Eventually, I got the edits done -- early too! -- but it was pretty much the only focus of my life during that time. I didn't work. I didn't write. I barely spoke to my family. It felt like all I did for two weeks was think about this book and make changes to it.
From out of my experience, I have put together a few tips to help anyone who might be facing their first novel length editing process, which I will be posting shortly. The key, I think, is patience and planning. Procrastination in editing is definitely your worst enemy. This time, I dove right in and I think I did a fairly good job. But we'll see when I get my next round of edits back.