I'm sure the variables are too many to count, but I have a decent review site that gets 22-33% CTR, depending on the landing page style I use. I've done some experimenting with longer LPs that do more preselling, where the CTR was lower but perhaps the conversion rate will be higher. Unfortunately the offer seems to have tanked and so I never found out conclusively. I've had LPs with much higher CTRs but very poor presell that didn't convert at all, so I think it's a matter of finding an optimal combination of elements. It can be a tradeoff in increasing your CTR and lowering your CR...
Some simple things that I found increase my CTR on the review site (and any site, really) are to make a variety of ways to reach the offer, since you'd be surprised how little some people know about navigating a web page. For example, I will have a product image/screenshot be a link, have a button-style image link, and also a plain blue underlined text link. This way, only a fucking blind alien wouldn't know where to click if they want to...