Wordscapes (Android)
Been playing this one for months on end, almost every day. It's a chill and relaxing crossword game, with literally thousands of differents levels, plus a new daily puzzle every day. For non-native English speakers it's also quite educational, as you'll inevitably learn new words -- I know I have, though most of those I haven't bothered to look up their meaning. :P
Apart from its entertaining and educational virtues, it's also quite aesthetically pleasing with its beautiful background landscape (hence its name) pictures. Being it a free game, it annoys you every couple of levels with an add, but you can easily avoid them by going offline while playing it (it wasn't a big problem for me as I usually played it at night in bed right before falling asleep).
I've had great fun with this game, but I've finally decided to quit it for two main reasons:
1) After thousands of levels it was bound to get repetitive, and it certainly did.
2) As of late, and after completing a puzzle (but sometimes even
during the puzzle), my phone freezed for quite a long time.
At first I put the blame for the freezes on the fact that my phone's internal storage was almost full, but after doing a bit of a clean-up and freeing more than half of its capacity, the game kept on freezing almost every other level. I still don't know what was causing the freezes, but I didn't want to enquire further. I just took it as a signal that I was done with this game and I unceremoniously proceeded to uninstall it.