If we compare the actual PC GPU, it's a good deal more powerful.   But we can't be certain if the are going to keep the clocks the same, increase them, decrease them, what the effects of the eDRAM will do, etc...

But, based on the knowns we get the following:

PS3's RSX : 190 Gflops
X360's Xenos :  240 Gflops
HD 4770:  960 Gflops

I´m a layman when it comes to that kind of thing, so if the Wii U´s GPU is indeed the HD 4770, does that mean it´s about four times as powerful as the 360´s GPU?...and about the RAM, how much are you expecting?...1,5GB?..2GB?

Relatively speaking, yes.   But because architecture has so much to do with how those gflops are applied, you can't take their figures at face value.  We'll just have to wait and see.

As for RAM, 1.5 GB should be enough.   2 GB more than enough.  Anything else is just silly.

Viper, since you´re so knowledgeable about that, first let me ask you..in your opinion, what´s the best looking game on 360/PS3 so far?...not really talking art direction, just pure graphical power (if that makes sense)

I'd have to think on it a while and really look into a few games. 

4770 was the initial rumor to being with because of its combination of power efficiency, modern die process and power.

No, I remember the initial rumor. It started right after the console was announced at e3 2011. A japanese website published the initial information and it mentioned that it would used a GPU that based around the 4850 with an indepentend tessellator.

It is also what popped up and every leak that I can remember. Seeing 4770 is a rather recent thing.

Ok, my question would be: with the best looking game on the 360/PS3 as a starting point, and taking into account (and assuming the Wii U´s GPU is the HD 4770 and its RAM is 1.5GB) the tech improvement offered by the Wii U, "how much better looking" would that same game be if taking full advantage of the Wii U´s power?...this might be a tricky question since I don´t know if you can put numbers here, like 'twice as better looking' or something like that.I don´t even know if I worded my question in a good way, I´m hoping you get what I mean.

That's a pretty difficult question (better looking is very subjective and difficult to quantify) but some scalable PC based engines should give you a clue to what new effects you can expect to see added on WiiU hardware. It's not simply a matter of being more powerful but what effects the chip architecture is capable of producing.

http://www.mycrysis.com/gallery/screenshot

The screenshots here should give an idea of how DX11 affects the look of a game... just make sure you download the full screeshots so you get a proper comparison. WiiU doesn't support DX11 (MS thing) as it'll almost certainly use OpenGL 4, but the same effects are supported on both and the GPU should support at least some of these.

Expect WiiU games to at least incorproate some of these effects to improve visuals over PS3/360 titles whilst retaining or increasing stuff like texture resolution, polygons and general shader effects