cheerless:used mainly to describe the weather or a room which is not bright or pleasant
helpless:unable to do anything to help or protect yourself
unhelpful:not willing to help other people
priceless:used to describe an object which has a very high value; it is worth so much money that the price cannot be calculated (compare with worthless below)
skilful & skilled:both can be used to describe a person who has the necessary ability, experience and / or training to do something well. eg He's a skilful footballer. This work was done by skilled craftsmen.
skilled:can also be used to describe a job or piece of work that requires special skill and training eg Nursing is a skilled job.
tasty:used to describe food with a strong and pleasant flavour
tasteful:used to describe clothes, decoration etc which is attractive and shows good taste
thoughtful:
a to describe a person who is quiet and serious because they are thinking about something
b to describe someone who thinks and cares about the feelings and needs of other people
worthless:used to describe an object with no value in money (compare with priceless above)