A user on NeoGAF has shared a series of posts that provide a relative understanding of the Wii U hardware in relation to the Xbox 720 and PS4. Supposedly, he is a developer who has proven himself to the moderators on the forum, but as with anything, be skeptical. It’s also very early days for the other consoles, so a lot of things can change between now and then.
This apparent developer compares the Wii U to a “low specs PC” and, while the “PS4 is not final yet and can change a lot”, the next Xbox is “more or less clear right now” and “the gap is big in almost every part”.
He specifically mentions, in response to someone disagreeing there will be a major difference with graphics that, “no, it will be noticeable (technically speaking)”. Of course, “noticeable” is a relative term in itself. But will be interesting to see if these systems make the Wii U look like another Wii in terms of raw power.