He's been a great player for Bioware so let's not forget his good stuff by association with the likely EA driven dreck and some people's inability to cope with varied sexuality.
He was the guy who's first boss job it was to make Neverwinter Nights interesting, and we got Hordes of the Underdark, easily one of the best cRPGs in the history of gaming for many, including one of the most beloved companions of all time, one that even Obsidian couldn't ignore for the sequel, Deekin.
He was lead writer for Dragon Age: Origins as well, a game which had many flaws but shined in its narrative structure which, without, could have left DA a dead franchise from the get-go.
For some he's the easy target for hate if there's anything wrong with post-EA Bioware games, but in most likelihood it was likely the EA business model which caused problems with those games. I've no doubt Gaider would be perfectly happy for his game not to have respawning bears, for example.
For others he the guy who 'forced' embarrassing and unwanted homosexuality in our faces, but I think it's safe to say that these people are not people who really understand roleplaying games so well if they perceive variety such as this problematic, right from a very base mentality if any game should have this kind of choice content, it's RPGs.
The reason for him leaving could be many and varied and let us not forget that the commercial environment is very unforgiving of age and does tend to get twitchy with staff at around the 40-50 mark, particularly in the tech world. There's also personal considerations, such as maybe conflicting ideals with superiors, a desire to have a few years out to go fishing, burning out, a desire to go self employed/do your own thing, the desire to spend more time with children/grand parents who you've barely noticed grow up/get to old to do stuff. Middle age is often described as the second adolescence.
So I'm just going to wish him well and thank him for making HotU great and for making DA:O bearable (and respawning bearless).