Holy crap that is a lot of sludge on that engine for only 75K miles? I would run so Seafoam or MMO in that thing for several oil changes to see if it cleans it up. All that sludge can't be good....
I also wonder why Drakken's is such a dark bronze colour. Is that the start of sludge? The aluminum should still be grey/white under the oil if clean... Then again if you look up higher a few more appear to be stained, including mine. Long as it's not build-up I'm sure it's fine.
What oil and OCI are you running? What type of driving do you do? Have you replaced your PCV valve?
As a side note, I admired how quiet and healthy sounding my engine was after the oil change this weekend. While in a line-up today there was a 2008-2009 GMC behind me making all sorts of noises, etc. Got to give it to Toyota for making a motor that runs well! I'd be nervous to buy domestic. They all fall apart. Even the Japanese ones made in N.A seem to be better.
That's varnish. I've seen that in lots of engines that ran a strict diet of dino oil, instead of synthetic oil. It's strictly cosmetic and not a problem.
Just an FYI, Singtoe's picture looks like it's of a V8 2UZ-FE, not the 5VZ-FE found stock in the 4Runner.