It is designed to keep you just interested, but not to find you a relationship. I guess if it did, they will lose business. In terms of this, this site (as well as most dating sites) is a scam.
1. Your message is not directly delivered. Your message is only visible to the receiver if they "like" you. I do not understand why any person would write a proper introduction to someone or more than a few words because the chances of your message being read is nearly non-existent.
2. The matching process is superficial. You're basically matched by the pictures and a small introduction, assuming there's mutual "liking" of these two criteria. As mentioned above (no. 1), there's no mutual selection happening based on a conversation. Looks do matter, but when there's profile after profile to choose from, the selection process becomes too superficial.
3. They do not show all available profiles in your area, so good luck if you live in a small town. Every time I refresh the browsing page, the same few people shows up. As I've found out, you must "pass / unlike" them in order to have a new person shown to you. Algorithms are against users in this case.
4. Difficult to find people based on interests because they only allow their own keywords under the search options.
Overall, I found Okcupid to be a huge waste of time, a platform designed to defeat the purpose it's meant to do from a customers' point of view.