That is a valid point, it really is. But then again, I don't remember the identity of most of the modern era shooters I've played. The problem with custom graphics is that the amount of work required to make truly good and recognizable visuals with staying power means pouring hundreds of hours into it. I've worked on this myself: check out Shinyshards in my signature, a work in progress. Those visuals are extremely simple semi-8bit visuals, but I probably spent around sixty hours tweaking them to get them to that point. And I'm not completely happy with them, and that's just one "tileset"; I need at least six more for the game. In the end, will it make you remember my game more than the platforming controls, the physics and the sound fx / music?
Again, you have a valid point there, and I certainly understand people who are sceptical towards the RTP resources--especially if they've been burned before