1. First and foremost, they keep sending you "checks" in the mail, that you can cash, and of course, have to pay off at regular interest rates. At best, these are merely annoying junk mail. At worst, they are insipid temptations to spend money - or be the victim of identity theft. I asked them to stop sending them to me, more than six months ago. But they keep sending them, and sending them, and ending them.
2. The interest rate sucks. Your typical Discover card has an APR of 13% or more, which is not very good in this era of single-digit rate cards. If you should ever have a balance on this card, the interest charges will be fairly staggering, which means you will have a hard time paying off the balance.3. The "cash back rewards" program, like airline miles programs, pays you back a pittance of the money they make on each purchase (2-5% from retailers) and you are supposed to give them blubbering thanks for getting $100 back after charging $10,000 in purchases. Sorry, but no sale. Like airline miles cards, these "cash back" gimmicks distract the consumer from the underlying fact that a credit card is a debt instrument, with an interest rate. While you may get "cash back" on purchases, the first month you don't pay off the entire balance, the whole savings from a year of "cash back" is shot. Better off to find a simpler card with a lower interest rate that to try to finagle one of these deals. In any financial transaction, the more complicated you can make the transaction, the easier it is to deceive the consumer. That is why credit card companies offer these complicated deals - PERIOD.
4. No one takes it. You have better luck getting an AMEX card accepted than a Discover card, or so it seems. What is the point of having a card that no one takes?