I love the Doodle Army 2 OR AKA Mini militia. Its the best game to kill time with friends. But wait official version is not much of the favorite of everyone. People love the Mini Militia game mod whic let them have unlimited health and ammo literally making it infinite loop of never ending match.
As a slight collector of ipad/iphone games here are a list of my favorites:
Fight List - This is my number one game that has saved me from more than a dozen doses of overthinking. It works really well because it gets you to list and think of different things according to a category which essentially draws your attention away from anything because you have to think about something else. Could not recommend it more. Give it a go whether its for fun or to distract yourself!
Threes - I've been playing this so much, ever since I got bored of 2048. I have a love-hate relationship with it as I usually play it when I'm feeling really down and bleh.
Neko Atsume - I've finished the game but it's so cute and I recommend it to anyone
Egg Inc - Super fun tycoony game! Very addicting and creative
Steppy Pants - Difficult but it feels amazing when you get the hang of it
Plants VS Zombies (1 or 2) - If you haven't played PvZ where have you been? lolol classic and super fun game
Zombie Tsunami - Fun game I've spent waaaaayyyyy too much time on
Tigerball - Somehow everyone at my school is addicted to this game? Very fun and challenging
Tomb of the Mask - Aracde like game, I haven't gotten to any of the harder levels but the start is kind of easy, its fun and arcadey.
High School Story - This has been my guilty pleasure game while I still had motivation to log in everyday, it's a little bit childish I guess but I've thoroughly enjoyed all the storylines and it's totally playable without purchasing anything.