A cheap has-been. If you're coming to Vegas to gamble and this is the best hotel you can afford, you probably can't really afford to gamble. Think about that.
Anyway, I'd give it two plus stars for being a decent, if sad, budget option, except for the bait and switch tactics the Riviera uses to lure those hotel shopping online: the base rate quoted on the travel sites excludes the $15/night resort fee AND is for a SMOKING room. "Upgrading" to a less gross nonsmoking option is an additional $22/night. So we're talking about a difference of $37/night between the online rate and the rate you actually have to pay.
Other than that, the rooms are decent but old, clean but shabby. The staff is neither friendly nor hostile but again, it's a cheap hotel. In a small town in the middle of the windswept prairie, this sort of hotel might pass for decent, but in Las Vegas this relic has long been overshadowed.