Because the 7z format treats these thousands of small files as a single solid block, extraction time is slower than ZIP, but the end result is a perfectly organized directory ready for modding.
Many users seek "highly compressed" to save on data. While these are common on file-sharing sites, be cautious as they can sometimes contain malware or missing game files.
“What do you want?”
This is the most devastating error. It means the largest file in the archive is broken. Fix: You need a recovery tool. In 7-Zip, select the archive, click File -> Test Archive. If it fails, you need a "recovery volume" (.7z.vol), which most distributors do not provide. Your only option is to re-source the file.