To me it's hard to compare Rival directly to a Shimano groupset. I think it's better to describe SRAM and Shimano's road offerings as different.

To me, as you move up Shimano's lineup, the components get slightly lighter, and shifting gets Smoother. With SRAM most of the lineup shares most of the features, and the focus is on low weight and functionality instead of smoothness. Where Shimano will smoothly move from one gear to another, SRAM will clunk into place, however that's not a bad thing.

If I were comparing cars, i'd say that Shimano focuses a bit more on luxury while SRAM sacrifices some of it for more performance.

For the price it's very hard to beat Rival, especially when comparing retail boxed SRAM to retail boxed Shimano.