Do 8 Speed Shimano Gears Actually Work Properly?
All my four bikes with deraileurs use shimano 8-gear cassettes. Although I have never had a 9 or 10 geared bike (I think it is too many gears, no need for that), I could say it works properly or not depending on many factors, mostly these:


If the cassette is worn, shifting gets worse, because the engagement points are not the same anymore;
If the deraileur has lateral play, same way: shifting gets a little less precise, although I would say this is not the worst problem, see ahead;
If HANGER IS BENT, then no matter what you do, shifting is terrible, as @user2839 said. If you set the upper gears to be right, the lower ones will be offset, and vice-versa.
Finally, if cable is not running smoothly inside the housings, there will be problems too.


But I would never put the blame on the cassette being 8-speed.

Hope it helps!