It is really hard to judge what would be a good CTR. It varies from industry to industry. There are things that you can do to increase your CTR like changing your copy or focusing your keywords better. Check out some of the previous strings on CTR for some tips on what you can do.
Really, you should be more concerned with your ROI. Are the people who are clicking, doing what you would consider valuable (buying, makinig reservations, etc.) or are they just leaving?