Bad customer service, illegitimate reviews.
Some time after I paid for a game, they figured out they were out of stock, so I didn't receive a serial. I sent a total of about 20 messages (felt like talking to a wall) before I finally managed to get a refund to my bank account (They wanted to give me a refund to my OKS wallet, which I don't think is acceptable, since I didn't want anything else from their store.) I've bought a few games with no hassle, so it depends on your luck, but the customer service is just awful. As for the reviews here, I don't think they can be trusted. I've noticed OKS posts on their facebook page that you can win a game if you review them on this website, so that's what causes the massive amounts of 5/5 reviews all within a short time period. Between January 12th and January 22nd, there are 300 reviews or so, and 99% of them are 5/5. While normally there's about a week between each review, and as you can see, most of those only rate them 1/5. Edit: Changed rating from 2/5 to 1/5 after they reported my review, even though I provided proof of purchase.