I know some folks really don't like Steam for different reasons, and I'm not entirely sold on them, but I know that for me, it just works. I am perfectly content with Steam, and I know that Steam has offerings in Windows, Mac and Linux environments, so things are pretty much covered there.
What I would like to see is WotC partner with an existing platform to deliver their builder rather than reinvent the wheel with a product they design themselves. On my PC, I use Steam, which also has app purchases and additional DLC. I am an Android user, and so I am used to app purchases as well as 'DLC' to get additional options. Since I suspect they will be more complex, I really would like the option, since it makes it lightning fast to make a character. First, if the rules are even as complex as the have been in the playtest, I want to see an electronic character builder. So I thought I would put my $.02 forward on what I'd like.
