Lethn summarize it all in his/her first post, games has become more a visual experience than actual game with challenge and stuff, I wonder how they dare to sell their crap at the price (like EA NFS stupid racing games, Code Masters which made worth games now than in the 80s, list is very long).
Competitions would be seen as a blessing more than a curse, as what they do, don't do, the choices they made, gamers' reviews, what they want, don't want, they like and don't like, just could help you in your design choices.
And as you're alone, if you're not good in 3D arts, you still could made levels like the prototype and make kind of Metal Gear Solid (PSX game) VR misssions (which was such a great success they release extra levels), this could be the free levels. Payments can be justified to get enough funds to pay for one or more 3D artist to make better levels for instance.
Finally, the worth things I experience in 3D games is the lack of sense, I mean we don't "feel" anything and there is no "substance" except collisions detection between player and objects/scenery. But Parkour and all those physical ninja like sports rely a lot on our own perception of the surroundings with all our body (our weight on one foot when jumping, the little slip of the shoe, the loss of balance then the need to do something to avoid falling down... all that kind of thing + more or less damaging injuries in some cases. If you can find something to make the character feel all those things, you may be far over competitors.
Games are all about design mostly but this big part has been left over by those AAA over funded companies, leaving the true root of video games in the void. IMHO, I like more a "basic" game like Putrid Shot Ultra or Nuclear Throne, than a 60 $ or more recent game I cannot play without spending thousands dollars on hardware. For instance all GTA/Far Cry are all the same at the end, just a bit more each time, full price each time. That's a shame. (FC3 & FC4 have even the exact same starting story ! What a hard work they've done there.)
Good luck with your project.