I can totally see where you're coming from. I assume you have never seen him play before he came to Milan, so I can totally understand that one would think "oh well, if that's all he has then what was all the fuzz in summer for?"
Those who have seen him play on his usual standards before know what I am talking about when I say that he has a lot more to give to us. Montella has destroyed him as he destroyed confidence and fitness of the rest of the team. Remember when he just arrived? He was on fire in pre-season, assisting and scoring left and right. In Serie A he scored too (I think it actually was against SPAL after a fk). Remember in the first couple of months of this season when among a bunch of horribly playing lads he was one of those who still had a decent run? My hopes are that Gattuso will be able to soon get him on his usual levels.
So if your question is what RR is about I can first tell you what he's not about: He's not the fast-pace FB who runs down to the line to cross or score, he'll never be that. Offensively he's more a slightly aggregated playmaker, holding ball in the 2/3 line and looking for that early-cross or cut-through pass no one expects from a FB. He also is phenomenal at shifting the play from one side to another with his long-passes. I mean just look at our 1st goal, how it arrived (timemark, 0:30):
He can do much more than seen lately, where he seemed very timid for his usual standards and I think Gattuso is very well aware of that as he stressed it out many times in the past that he thinks RR can do more.
Defensively he usualy is very composed and calm. His strenghth are actually his very well timed tacklings. He rarely lets an attacker go because of his exceptional timing, which makes up for his lack of pace. I remember games when he had Messi or Di Maria in his pocket and speed wasn't even an issue. Sadly these days it's not the RR who is defensively so confident and almost flawless. Lazzari was on fire, true, but that shouldn't happen that he can overrun RR so easily. RR is also very good at holding the ball, you can see that he rarely looses a ball to the opponent, even when under pressure. Finally, even when you don't see him sprinting all the time, he's in almost every game of ours in the top 3 of km / game. He's not afraid of doind the dirty work. Very valuable asset.