My impressions are more or less in line with our impressions from January. I tried out both Portal 2 and Broken Age. The circular track pad does a decent job of recreating mouse movement in Broken Age, though the sensitivity could make it difficult to settle the pointer on dialogue options (I wasn't able adjust sensitivity in my demo, which could alleviate the issue).
Using the thumb pads in Portal 2 proved much more challenging. Precision aiming when firing portals, especially when I had to make portals on a distant surface, was tricky. Four way movement was a little awkward as well, though I was pleased that my position on the thumb pad simulated analogue movement, allowing me to move at a slow creep or a quick run. The haptic feedback in both pads also helped create a feeling of resistance, though obviously it won't fool you into thinking you're using an analogue stick.
It's impressive that the Steam Controller can bounce between styles as disparate as 2D adventure and first-person puzzling, and its touch pads could become second nature over time, but it's definitely not going to provide a seamless transition from traditional controllers, at least not in its current state.