It is true that new US players can join only via invitation. And it's also true that those invitations are hard to come by, and you won't get one by asking on a public forum. And just to be clear, not just any player can invite you -- only certain players are granted US invitation privileges. If you try to sign up from a regular player invite, your account will be created but then suspended and you won't be able to login or play.
I can tell you the action is pretty poor right now, because they've just recently been forced to adopt a strict segregation policy due to certain other skins on the network not paying their debts. Intertops is without doubt the most well-run US facing real money poker site
left, and my hope is that they're preparing to leave the Revolution network. I just don't know where they'd go -- ideally they'd go on their own, but starting from zero player liquidity might be a problem. Merge and WPN are the only remaining networks allowing US players, but Merge has been dropping their excess skins and WPN's software is the worst of all of them IMO.