I'll cut right to the chase and openly state that Diablo III's couch co-op is about as good as it gets on consoles and it's all thanks some brilliant design work on behalf of the dev team responsible for the port. I can't remember the last time I've been so pleasantly surprised and impressed with a very PC-centric genre port to consoles.
Diablo III's user interface is really where the game shines and could easily set the standard for future PC ports of action RPG's. PC centric genres that developer/publisher Blizzard specializes in are often very difficult to port to consoles due in part to the limited button set of console controllers. It's why we see very few console MMO's and even fewer console RTS games. There has been some success with the action RPG genre on consoles in years past (Baldur's Gate Dark Alliance, Champions of Norrath) but nothing comes close to the excellence of Diablo III.
The tab and radial system used for menus in the console port is unquestionably the best that any console action RPG has ever implemented. It makes navigating individual player menus, changing gear, and equipping skill sets just as easy and efficient. It's lean and clean in a way that few PC-centric players like myself would have expected. During frantic four player couch co-op sessions it was quick and easy for players to take turns to equip newly acquired gear and drop class specific gear for other players. The fact that so little time was spent meddling through the menus is a testament to design team's brilliance in implementing a smooth U.I. that never feels like a chore.
Diablo III's control scheme is equally well adapted and every person I've played couch co-op with so far has picked it up and mastered it within minutes. Characters move around with the left thumb stick, can instantly use preset items with the directional pad and have all their abilities just a single button press away with the shoulder and face buttons. It's so easy that it's shocking no other developer has got it so right up until now.
Just as easy is the ability create a character and store their items and data for future play sessions. Players can choose to store their characters locally on the console or link it online with their own gamer profile. It's very efficient and simple to use and ensures that I can have a friend come over months from now and pick up exactly where we left off, even if two of us have leveled up a bit and progressed through the game separately during that time.
On the technical end, Diablo III on consoles may not have the fidelity that players will see with a dedicated gaming PC, but it definitely holds its own even when the screen is flooded with enemies while all four characters spam their best abilities. The frame rate stays at a pretty solid 30 fps and individual character abilities retain the unique and graphically impressive nature they enjoyed on the PC. Console players will certainly not feel like they are playing an inferior version.
More suprising is how the loot drop mechanic seems much better on console than it did on PC. Players are no longer flooded with mediocre loot that they have to constantly sift through on the inventory screen (something that would kill any sense of flow that comes with couch co-op). Loot is more sparse while simultaneously being more relevant, perhaps not by a great margin compared to its PC counterpart but enough to cut down on any tedium.
I would say that the console version of Diablo III is now my preferred version simply due to the couch co-op. Playing as a team sitting on a couch and yelling frantically at the screen as a group while tossing back root beers is too rare an occurrence in gaming. The tight U.I. is just icing on the cake. It makes Diablo III one of the easiest recommendations this year.