I’m a pretty skeptical fellow but I must confess to being impressed by some of the work that has been done in osCommerce Phoenix. In particular, building templates using content blocks enabled by admin was an inspired choice.
For modders, if you make the handful of changes described in my Phoenix Tweaks page, your old osC 2.3 code will likely work, but a better path is to adopt Phoenix standards and just update your code.
I have taken the latter approach in Better Together for osCommerce Phoenix. I look forward to updating my other osCommerce modules in the coming months.