One of my older, but seemingly well-liked projects is sitting at around 2.27% CTR from 88 impressions in the last week. I think that sort of percentage is good, though they can range wildly. For instance, one of my newer games has 0.91% CTR from 11k impressions in the last week. Likely, most projects, even if they are stellar, will fit within the 0.9% to 3% interval because it will require some top-notch advertising to the right people (or just some really devoted fans) to get a high CTR in most cases.