You can actually find
a lot of Final Fantasy games on Google Play. SquareEnix has been
pretty active on Android. I don't know what you mean by "more open", but I would definitely recommend you tried
Chaos Ring. It has a cool innovative fighting system. You could check
this Youtube video to get an idea of what you're stepping into.
If you're a fan of the old FF games, I also recommend
Final Fantasy Dimensions. It's a brand new game that was developed with the look and feel of old 8-bit games. It's really cool.
Free games are more difficult to come across. Most "free" games will pack in-game purchases that seem optional but are necessary to enjoy the game, even a little bit. This is why I prefer paying upfront.
The one free game I came across which is enjoyable even when ignoring in-game purchases is
Zenonia 5. I haven't played the rest of the series, but Zenonia 1 to 4 are available on Google Play if you want too.