Multi-item listings is the worst thing they've ever done because they totally ruin search results.
Let's say you're searching for something like a box of 200 disposable gloves. You dutifully type in "200 gloves" or "100 pairs gloves", filter by "Buy it Now" and sort "Price Low to High".
Suddenly your search results are filled with dozens of pages of results all priced at $0.99. How could a box of 200 gloves be so cheap? Because it's not showing results for 200 gloves... it's showing you a multi-item listing which contains packs of gloves in several quantities. One option is indeed a pack of 200 gloves, but that's priced at $20. The $0.99 option is, in fact, a single pair of gloves, listed as a "Sample".
You can't exclude multi-item listings from the search results, so this leaves things very much open to exploitation by unscrupulous sellers.
This makes the search basically useless for anything which could be sold in multi-item listings. It makes eBay unusable for me whenever I'm buying anything except for unique, clearly-listed items.
Another point of frustration is that you can't filter by shipping speed. Some listings boast a "Fast and Free" label which indicates that the item will be delivered within three days, but you can't actually filter on this in the search results. So if you need an item quickly, you just have to manually sift through all the results for items labelled "Fast and Free".
If any developers from eBay happen to read this comment, I'm available for hire as your personal rage and frustration consultant.