I took a look at Deep Green to see what all the fuss is about, and yes, there's plenty to talk about - Deep Green is beautifully made, with its felt green background and seemingly carved icons that jiggle about the screen, throwing overlays across the board in tasteful swathes.
It would look like everything is there. All the nitty gritty rules can be modified and viewed for hardcore chess players. Undo? Of course. Hints? No problem. Setting two high level "Deep Green" computer opponents against each other? Well why didn't you say so!
But then there are things that are a little bit strange, like being able to manually set up the board yourself. Piece by piece. Dragging and dropping. The inclusion of features like this don't hurt Deep Green but honestly is this something that people do?
Everything you could possibly want from a chess game is there apart from one thing, and that is networked multiplayer. Groan if you like, but playing against a computer - no matter how many settings can be beautifully turned about - just doesn't seem like all that. When playing against a human opponent there's a certain thrill, a sense of engagement. But with computer opponents, even on the low levels, chances are the AI is going to soundly defeat you. Sure, that's said from the perspective of people who just play Chess every now and again, but it's safe to say that that's most people. $4.99 is okay if you're a serious chess player looking for a deep version of the game, but even that's an introductory price which will go up to $7.99 when the new year comes round.
It seems a little unfair, because Deep Green is really really good. It's got the looks, the depth, but misses one of the main advantages of the iPhone: it is a networked device. Stood next to Chess with Friends (which is free), I can easily imagine the choice for most people interested in a Chess app would be a fairly simple one to make.
If Deep Green adds networked multiplayer and stayed at its current price, its competitors would have to really step up their game.