One thing you have to keep in mind is, everything changes. If you had bad luck with them before, give them another go. Dynamic Search Ads have gotten to be better than what they used to be. If done right and optimized correctly, they can perform extremely well.
Sam Owen has confessed that he was not a fan of Dynamic Search Ads at first, but had his mind changed after a presentation by Matt Umbro at SMX West. Because of his change of heart, Sam wrote an article on Search Engine Land that shows how to run a successful Dynamic Search Ad campaign.
To check it out, you can visit Search Engine Land, or visit his article directly by following the link found below.
Search Engine Land: Why AdWords Dynamic Search Ads Work Better Than You Think