They are a ripoff. however i would not call them a scam since they seem to actually have a mining farm going on, so at least they are not just a ponzi operation. However, that doesn't make them profitable by any means.
Genesis mining is mining hot air. If they are as they say they are, and that's a big player in the mining industry, people should be able to see the addresses their block rewards are being sent to.
And exactly this is something that doesn't seem to exist. People from the very early days years ago, have been asking for their mining addresses, but genesis mining blatantly ignored all people looking for this information.
Genesis mining is in fact a ponzi, and one with a solid amount of marketing behind it. This explains how they manage to continue paying people out, because as long as fresh money comes in, they will remain operational.