I can't speak for his time on Hollyoaks, as I'm not a regular viewer...
However, he was absolutely dreadful when it comes to EastEnders. After an incredible 3 years under DS, he completely butchered the show, and it still hasn't and probably never will fully recover!
Finally enough, I think his first few months as EP were brilliant. Bringing back Lisa Fowler, and Phil's drug addiction were great ideas, as was bringing back Kat & Alfie to replace the hole Peggy left. Stacey's exit episode was flawless, and the fact it was watched by over 11 million people hopefully echoes that. The Queen Vic Fire, Peggy's exit, and Billie's death were also handled fantastically. I enjoyed the Janine/Ryan/Stacey plot, and loved the introductions of Vanessa and Michael. But, like others have said the guy has no long term vision, and after a few months of great consistency under him, the show started to dip. The baby swap storyline was very controversial, but delivered some great drama. After that, things just got worse, until the show was unrecognisable. After a very strong 2009/2010, 2011 and 2012 under Kirkwood were a complete mess and a disaster, not to mention killing off Heather and Pat were awful, awful decisions... Epically the latter!