Generally a lot more toffee/caramel/toast and often slight roastiness in a Red IPA vs IPA. Basically much more malt backbone to accompany the "in your face" hops.
One significant advantage IMO of Red IPA vs standard IPA is once the beer has aged slightly and the hop intensity fades. With a standard IPA you are often left with a very bland beer, with many RED IPA's you are still left with an equally delicious beer. One example that springs to mind is Heretic Evil Twin.... fresh from the brewery it is incredible; the cans we get have some age on them & we are still left with a delicious beer which is quite different to the super fresh version.