The opposite of "quality" (of fine material or construction) would be inferiority or shoddiness.
The opposite of quality papers would be poor or low-quality papers.
The opposite of a lofty quality would be a mundane or ordinary quality.
good quality
good quality
expensive opulent, expensive, pricy, highbrow,
low mortals least value
For comparing quality, the opposite of "premier" (superior) could be inferior or poor. Where premier assumes the very best, the opposite is worst or poorest.
The opposite of better (improved, superior) is worse.A similar words for "of a lesser quality" would be inferior.
The opposite of "improved" is "worsened" or "deteriorated." When something is improved, it means it has been enhanced or made better in some way. Conversely, when something is worsened, it means it has declined in quality or performance. Therefore, the opposite of improved is a decrease in quality or value.
For most meanings of good, the opposite is bad, or possibly awful.For good meaning "benevolent" the opposite would be evil(malevolent).For good meaning "acceptable in quality" the opposite would be poor.For good meaning "fresh" the opposite would be spoiled or gone bad.In other applications, the opposite could be unacceptable, unsuitable, or useless.
The prefix that makes "upgrade" mean the opposite is "down-," so "downgrade" means to lower or reduce in quality or status.
Durable good