I see bad things looming for Ronnie, which is a shame because I always liked the guy, even if it took him 6 years to step out of the edge of the frame. He strikes me as having (at least) the smarts of Vic without his, and to some extent Lem's, self-deception, while never exhibiting the arrogance or sadistic tendencies of Shane. Also, the poker player in me appreciates that while constantly lying, he doesn't go for the complicated or falsely emotional route of Vic/Shane, but remains generally stoic and reticent at all times, which means he doesn't give away much when, say, the partner he set up to have killed shows up at the murder scene (loved his resistance to Vic's change of heart, btw).
Random thought: I often see the Shield compared to the Wire. Don't worry, I have no desire to rehash the sizzle vs. steak argument, because I don't think they're actually similar beyond the utterly superficial level of featuring cops. Rather, I think the show's actual HBO cousin is the Sopranos, as more than being a Cop Show and a Mob Show, both are very much Liar Shows. It seems, especially as their respective seasons added up, that every scene has someone hiding their true reaction to whatever is going on from someone else. It's impressive that the casts have done such a good job of it in both cases, as I imagine that one of the most difficult things for a professional actor to do is act like an amateur acting.