In my personal opinion the more we go on, the more good graphics will be determined by designers skills, the less by hardware capacity. Current HD console are already capable of rendering almost every imaginable scene with a good level of detail, and every year I think the average graphic quality of games gets better, this means Ps3/360 have not yet reached their potential limits. Next-gen will improve that but only marginally, probably we will see a relevant difference on large scale enviroments, but the fact is that not every game needs a large scale enviroment. So the more the hardware will go on, the less games will get a real benefit from it. The hardware will continue to evolve, but our perception is always the same, it is limited and also subjective.
An example of that may be comparing Mario Galaxy 2 with Darksiders 2 (Wii and Wii U games). Darksiders 2 is a much more complex game in terms of graphics it's obvious, and there is a generational leap beetween the two, still I'd say Mario Galaxy 2 has better graphics without thinking twice. Why? 2 reasons: 1st I like the SMG art style more (a subjective reason) and 2nd beacuse a game like mario doesn't need the same amount of power a game like Darksiders needs to look good. An example of perception may be this one:

You can add as much complexity as you want, but afer a certain limit you won't notice the difference anymore (30 in my case), you can apply the same to texture res. That's not to say we won't see a leap but it won't be something as substantial as Ps1 to Ps2 or Ps2 to Ps3.