Engadget went hands-on with the Wii U Pro Controller at E3 2012, and also shared a couple of high-quality photos (one of which is shown above). As for what they thought of the controller itself, this snippet explains their impressions the best:
…the controller seems to be slightly wider and a bit shorter than the 360′s. The unit’s ergonomic shape and button layout proved very comfortable during our session, not least of which included its fairly sturdy feeling build quality and light weight.
But if you want more depth, you can click here to read their full preview.