It’s a relative term - what one individual may consider to be cruel and unusual may be different than what another considers cruel and unusual. I think it’s the perception of pain and suffering of the convict - is immediate death assured by a firing squad - probably not. Lethal injection is supposedly more humane although there are many detractors of lethal injection as well who claim it is cruel form of punishment.
If we bring Islam into the discussion, while punishment for immoral/illegal acts is written, punishment should not be malicious or cruel - a criminal should be treated with compassion and “anything and everything” would not be acceptable.