I don't have one myself, but a friend of mine works at a gun shot and happened to have the Ruger on the wall next to a Smith & Wesson M&P 15 Sport and a couple of other comparably priced ARs. I have an original "first generation" Sport that had a 1:8-twist barrel but no forward assist or dust cover. Then S&W changed to a 1:9-twist barrel, while Ruger introduced the AR556 with 1:8, forward assist and dust cover. S&W then "caught up" by adding the forward assist and dust cover to the new Sport II model, but stuck with the 1:9 barrel. The significance of this is that faster twist rates (1:8 and especially 1:7) have increased in popularity among people wanting to use heavier bullet weights in their ARs. You may or may not care about this yourself, especially since heavier tends to equal more expensive, but twist rate is a factor for many buyers. That alone may make the Ruger more attractive to some.
The fit and finish of the AR556s I've seen seemed equal to others at around the same price. The rear flip-up sight is different from a Magpul MBUS but similar, and the A2 front sight is serrated, which I haven't seen before. The handguard and stock are the typical generic style. Not much to differentiate the Ruger from its competitors. If the warranty is a good one, that might be a deciding factor, but I haven't looked into it myself.