I would think that you would need to hit some of the underserved genre/subject niches to be successful. There are a bajillion dungeon-crawlers, military shooters, 4X fantasy/space games, 2D platformers, fantasy rpgs, casual puzzle games, zombie survival games, etc. These combinations have a lot of widespread appeal, but the market is really saturated.
The thing with niche genre/topics is that most of the successful players have a pretty established track record of delivering an above-average product - see Paradox, the Close Combat series, many of the hex-based wargames, the author of TFA. There are also in many cases established classics that are timeless, so if you're going into that space, you need to either have an interesting spin, or really outdo the classic. Just building a clone isn't going to get you very far.
The thing with niche genre/topics is that most of the successful players have a pretty established track record of delivering an above-average product - see Paradox, the Close Combat series, many of the hex-based wargames, the author of TFA. There are also in many cases established classics that are timeless, so if you're going into that space, you need to either have an interesting spin, or really outdo the classic. Just building a clone isn't going to get you very far.
It might be interesting to build something like one of those old hack author plot-wheels for indie games, based off of this: http://gamedevtycoon.wikia.com/wiki/Game_Development_Based_o...