Why does Impressive have a bad name?
Impressive carries a negative connotation only to the misinformed and uneducated.  The great stallion did carry a gene which had the potential to cause a severe health issue known as HYPP.  For more particulars on this disease please google hypp and look up the details.  Impressive was considered one of the all time leading Quarter Horse sires until this genetic problem was made known.  The problem was so severe that AQHA started requiring all Impressive bred horses to be cleared as not being capable of passing on the gene in order for their foals to be registerable through the AQHA.  A simple blood test was developed and all responsible breeders are sure to only breed those horses that come back with a n/n rating - therefore if a horse is rated n/n there is NO CHANCE of him/her having or passing this disease on.  Once a horse is determined as n/n is is the same as any other horse - no better - no worse.

What makes an Impressive bred horse desirable?
Despite the hypp scare of the 90's Impressive bred horses are known for their outstanding build and their great temperaments.  They are usually extremely easy to teach and equally willing to learn, they are easy to get along with and they look good doing it.  There is nothing mediocre about an Impressive bred horse.  There is a reason why Impressive was one of the leading QH stallions - his foals were outstanding and much in demand.