Those of us who aren't too big in the technical world of computers likely don't appreciate what an achievement this is. That said, I'm sure everyone can appreciate a guy putting in the hours to make Wolfenstein 3D fully playable on a Game Boy Color!
Wolfenstein 3D has appeared on Nintendo handheld before...but it was on the graphically superior Gameboy Advance...and dare I say not as polished as this work of art above.
For those more curious about how he did it, here's a snippet from the Engadget article that better details the technical side of things...
"Granlund used a breadboard to program the EEprom himself, then ordered a custom board, complete with pinouts. Using those, he added an NXP graphics processor, equipped with an ARM Cortex-M0 running at 48MHz. That chip is obviously more powerful than the Intel 386 CPU that originally ran Wolfestein on MS-DOS."
I don't understand it, but I respect it! Now do something like Morrowind!