Asterash is a small free to play game I released on Newgrounds. It's made in Flash and, while it is a non-professional project, it was meant to be a challenge both for me and my teammate Monoflauta (Facundo Balboa), both in terms of tech and design. Regarding design, the game had to be attractive and polished enough to guarantee several runs per player, since each run showed the user an ad.
What I chose to do in order to accomplish this was to base the game on randomized elements, minimize the downtime each time the player died (and the ad was shown), and finally putting something he could aspire to in the form of an ever inflating scoreboard.
After some feedback, we realized people wanted a chance to pick their starting weapon, since they quickly developed favourites. We released a patch shortly after launch that allowed them to pick if they watched the ad long enough. It is a pretty common practice that we decided to avoid at first, considering it could be invasive to some people since death was made instantaneous, for obvious reasons.
Eventually we decided to give players both the chance to play again without any control on what they got, or wait an X amount of time.
The game was an instant success on the platform, and it made money, which is a remarkable feat for this kinds of games since the fall of Flash and its game portals. Runs started at more than 10 per player, before settling in a bit over 8.
We also managed to retain several players that would often come back to keep trying to move onwards in the leaderboards. This, for us, was quite an important thing, given that most games on Newgrounds and similar platforms these days have an extremely low retention of the players that come to have contact with them.
This is what free to play is about, for me. The game needs to work, it will have goals that the developer is trying to achieve, but at the same time there's nothing preventing people from enyoing a free to play game.