Hello Makuto
I've had similar expieriences with what you are describing and asking.
In fact my first post brings it up to a certain degree:
My ideas were developing to some extent since about 2001. They took a sudden halt when I found a game that had almost all of the things I originally sought after while designing and conceptualizing. I no longer felt the need to develop a game with some concepts which weren't mainstream due to this game. That game was Fable, with its announcement my ideas seemed to have been played out closely enough. A lot of the things I had wished for were coming into the industry in one form or another so why should I keep developing them? Others would eventually think of everything I had so why not sit back and enjoy it right? I didn't feel cheated or bitter as some would think when it was released, I was glad I could enjoy the things I wanted for so long.
Like you said, theres nothing wrong with seeing where other similar games succeeded or where they were lacking. I mentioned this too within my first post:
After playing Fable (and eventually all of its successors) I realized the experience was satisfying but didn't quite quench my thirst. It added loads for me to build on and furthered many of my original concept. Yet, I still felt I had more to offer.
The things you feel were done correctly can be implemented within your design, built/expanded on, and ultimately (ideally I should say) you will further innovate (or at the very least tailor to your liking) what others have already proven to be a good concept. If you feel something was lacking and could be improved, that there is your motivation. It will be the reason for exposing yourself to similar concepts to begin with. As everyone has unanimously agreed, exposure and experience with things similiar to what you have envisioned/wish to create is one of the ultimate tools. If you know where others have failed and where they have succeeded you get a clearer web/map of what you should/shouldn't do.
Hope this proves useful,
Sin ?§•??§?