Again this is just my opinion as a fan.
Dan Didio also seems to have a great passion and love for the artform. When I saw him at a couple of convention panels and I have read his remarks in interviews and his weekly column he seems to be a sincere individual with a love for the artform. Also under his tenure DC has re-invigorated their entire super-hero line. In total I have to say that I think the over all line is in the best shape it has been in a long time. Getting to that point was often painful and I think that until we hit the One Year Later jump I was seriously doubting Dan's vision for the super-hero line.
Under Dan's leadership they built-up to Infinite Crisis and have essentially relaunched every super hero title in their line with the one year later jump and have launched and succeeded (so far) in producing a weekly comic (52). While every issue of 52 is not a home run, it is the book I want to read first every week. Also under Dan serious talent has been put on the main two characters of DC Batman and Superman. It is the first time I have been buying Superman for years and Batman has been very good for the first time in at least 10 years. I think it is important that DC's most recognized characters are also well done books, by strong talent. DC has a slew of solid series Aquaman, Atom, Birds of Prey, Green Arrow, Firestorm, Green Lantern, Teen Titans, Outsiders and more are all good entertaining comics month in and month out. The various mini-series as opposed to launching a ton of ongoing series is also a move I agree with. Too often a series is launched based on one or two good concepts and then flounders and dies. This way we have the ability to spotlight characters that would no warrant an ongoing book. Of those Spectre, Secret Six, Mystery in Space, Martain Manhunter and Uncle Sam and the Freedom Fighters are good series that comes to mind.
We have had some spectacular failures and the worse one of all is a core DC character - The Flash. This book was so bad that is should not have been published. The Wonder Woman relaunch has been bland and the first couple of issues of the Ion maxi-series were very poorly done. Ion has picked up and I hope that Flash can improve.
Another gripe I have is Dan's idea that Bruce Wayne will always be Batman. Superman is an alien so he can age ever so slowly, Wonder Woman is tied to the Olympus Gods and can have immortality that way, but Batman should age and Dick Grayson should take over as Batman. Dan has a similar trait with Joe Q. Over at Marvel and that is they think there characters are timeless for certain core characters and that means they adjusted reality to work around these characters. That causes too many reboots and too many fast and loose interpretations of continuity. Be bolds and daring and let the human characters age.
Another complaint that I have is that it seems like Elseworlds has gone by the wayside since Dan has taken the helm. These are the type of stories that have created the best comics has to offer - as Watchmen, Dark Knight Returns, Kingdom Come and New Frontier are non-continuity projects that allow free reign to do what you want in the DCU. The amount of these projects was overwhelming, but I feel like those projects are no longer being sought.
All in all I believe Didio has done a good job in handling the DCU and has focused on making each book the best it can be. Also when he makes a mistake (wanting to kill Nightwing) he at least had a logical and good reason for why he wanted to do it and is now challenged his people to make Nightwing more of a central player.
I have been more of a DCU fan then Marvel for a long time now (although the Silver Age Marvel was my first love) and under Didio I don't see that changing.