The logic behind the method is that your face produces oils for a reason, and so it makes no sense to completely strip all of those oils away and then try to replace the natural oil-based moisture with a water-based moisturizer. Traditional, commercial face-washes and astringents and acne treatments can be incredibly harsh on the skin, and operate on the principle that "oil is bad." Too much oil sitting on your face all the time isn't ideal, but oil in and of itself is good for your skin. If you aren't stripping all of it off every morning and night, your skin won't feel the need to go bonkers and overproduce its own oils, which is where that "greasy" feeling comes from.
I won't lie, oil cleansing takes a bit more time than regular face wash, but it feels so good and your skin will be so happy afterward. Well, probably. It doesn't work for everyone, but different oils have different properties, and if a certain blend isn't working for you, another one might do much better.
Castor oil is used to pull things (like blackheads) out of the skin and dissolve dirt. It's a fairly heavy oil, so if you use only castor oil, it's going to be hard to get off your face. That's why most people cut it with a lighter oil, such as olive oil, which helps to dissolve makeup as well as making it much easier to remove the oil blend with a wet washcloth.
I have combination skin, so parts of it are dry and parts are oily. My personal blend consists of (approximately, because I don't measure) 50% castor oil, 40% olive oil, and the remaining 10% is varying amounts of jojoba, grapeseed, and sweet almond oil. I also put in a couple of drops of lavender essential oil for smell and its antiseptic properties. I massage this into my skin for a few minutes (or longer if I'm zoned out and watching TV or something while I do it), then I wet a washcloth under hot water, wring it out, and lay it on my face. This is possibly the most relaxing thing on the earth. Then I gently wipe off the oil and, if my face feels a little dry afterward, pat on a few drops of jojoba or sweet almond oil.
This worked beautifully for me all winter, but over the summer my blend was too heavy and I stopped using it. Now that it's starting to cool off again, I broke out the oils and have started it back up. I wish I had never stopped! My skin looks better and my breakouts are under control, and the scarring on my cheeks has lightened considerably. I also find that these oils last so long and have so many other uses, I feel like I'm saving money over buying a little $8 bottle of Neutrogena or whatever. It's a larger upfront cost to buy the oils, but I think it's a good investment.
There are tons of resources available via Google if you want to figure out which oils work for which problems. A bit of searching found me this thread about essential oils and their properties from a forum apparently called Essential Day Spa or something.
If you give this a try, let me know how it works out for you! I cleaned out the bathroom closet today and found an old bottle of Sea Breeze astringent and I can't believe I ever put that stuff on my face. The smell of it makes my soul cry.