First list as many Genre's of games as you can. Then spend a day for each genre researching what gripes people have with that genre. Then after that you should have some idea on what can be improved better for an easy game and an idea of where to fit a game in the market. Trust me if you do a nice job and you've picked it well and sell it for a couple of bob a piece. Don't do a free version with in game purchases unless it's a big game it put's a lot of people off and doesn't stand well in the crowd.
If you want more sales than get your logo on something completely free simple and desirable just to get your logo running on lots of devices and if you do a good job you will get the attention for sales of your other game. being more advanced is not an essential feature of what people buy it's a big bonus but not essential. It's better you do a good job with your game than focus to heavily on what would take a big team of people to try and pull off if your alone or in a small group. If you are gambling with a few people to make a 3D game then Focus on portability, 3rd party upgrade-ability and hitting the base line of what you need for the game to hit it's mark in terms of game play with a consideration that if the game is Liked other people will make the game look better.