I wonder how long it took him to make those enviroments (In the OP.)?
"Professional" games basically "require" teams of 100 people, along with many, many millions of dollars and years of development time at the moment -- not to mention that they are already saying that future games will cost a lot more and require more people -- yet with an engine (Which many development teams also start out with nowadays.), the results of 1 dedicated person compared to a huge team aren't all that different. Atleast not as different as anyone would expect.
I'm not just referring to the OP; there are obviously many more factors to consider, like many more levels/models, NPC's, scripting, voice acting, A.I, physics, animation -- but still, there are entire games made by 1 person out there.