In my opinion, if it is a mass market platform (desktop, mobile, web)- it does not really matter where to publish. What does really matter is how you conceptualize and integrate your business model into the gameplay, which should be designed with your target group in mind.
You should consider this questions first:
- Core game play (e.g. if you wanna reach a mass market you should go for super-straight forward things, interactions should be clear, no frustrations, but the gameplay should be meaningful and with depth)
- Setting: gfx, story etc. There are some rules of thumbs like polished and straight gfx, progression indicators etc, no SciFi or fantasy.
- What is your "viral" strategy?
- What is your business model (how are you going to monetize)
- Metagames are the most important (user retention & engagament) There are some good examples of games in appstore, which are great because of very well designed metagames (e.g. Puzzle Craft)
There are many games in appstore and google play, but only may be 10-5% are vere well designed products. There are tons of nice and easy games, which are easy to pick, but the lack depth and you throw them away after playing them a couple of times. So I think there's always room for cool stuff, no matter how saturated the market is.