I love Kingdom Rush! It's also available for the iPad, but is originally a browser-based game.
Crohn's disease troll here!
When I'm doing bowel prep (which I'm doing all the freakin' time), my favorite thing to do to pass the time is to play tower defense games like Kingdom Rush - http://www.kingdomrush.com/
Really helps make the time go by faster.
i really liked kingdom rush, first bought for my mobile but its also fun on pc.
http://store.steampowered.com/app/246420/
http://www.kingdomrush.com/home.html
it's not for sale at the moment but not to expensive as well
For PC and consoles, I can personally suggest taking a look at Warframe.
On mobile, I'm currently enjoying Fire Emblem Heroes, and the original Kingdom Rush is a good free introduction to the games.
Kingdom Rush
YOu have to try that!!
You can play if for free on PC as Flash game:
http://www.kingdomrush.com/ http://armorgames.com/play/12141/kingdom-rush (Play for Free on PC)
http://itunes.apple.com/us/app/kingdom-rush/id489265199?mt=8
Runescape Mobile, but there's not much point in playing it if you don't already playing Runescape.
In terms of games, yeah, I've mostly only ran into gacha games, which is usually the case with games with an anime artsyle. I haven't played it on mobile, just on my PC, but Kingdom Rush is a decent game with a flat up-front cost of $2 or $3. I imagine most of the good, non-gacha games will have a flat price.
From your message I coudn't quite make up if you are also interested in good web based games?
Like:Agar.io or ~~Kingdom Rush~~ (apparently is not web based anymore)