I play or have played CoC, CR, HD, and obviously Boom. If you dont know by now, I believe the term for these games are called pay to win. Sure its free to play, but once youve reached a certain point, youre either waiting weeks to do anything, or the bases / operations you can attack reach a difficulty level and time constraint that demand you pay (or quit playing essentially). Ive got no problem paying $60 for a console game, and $20-30 for an expansion pack that takes me hours and hours to complete. I would feel the same about all of Super Cells games if it seemed like $50-100 and I could be a top player. It is alas not. I have spent roughly $50 "gemming" which I think is fair tribute for the hours Ive played....but I am no where near the top. To catch up to even where I am now if you start playing today youd need to drop well over $1000. For me to catch up to a level 63 player, Id be in the $5000 range.
That all being said, its a fun waste of a few hours, and its bite sized fun is sufficient enough that I would recommend playing it, maybe dropping a few bucks on gems, just dont get yourself in it for the long haul.