I have to come out clean, i am not really an avid gamer anymore. I quit hardcore gaming at the PlayStation 2/3 boundary and haven't played any console game since February, before that i hadn't played any for year. So that's my full disclosure.
1. DEAD TRIGGER 2
I have had this game on my phone for over a year now, it's basically my favourite game on Android. Dead Trigger 2 has amazing graphics and great gameplay. And you get this at the great price of FREE with in-app purchases, which you don't need if you are a old school gamer and believe that games should be challenging.
2. SKYFORCE 2014
If you owned a Symbian device before 2006, you ahould probably known this game. It was by far the best game on Symbian S60 and UIQ, unless you had the N-gage or figured out how to install N-gage games on phone. SkyForce 2014 on Android hasn't got the best graphics (but i's still good) like it did back on S60 but the gameplay is just as engaging as it was back then.
I think it's mandatory for everyone to have a puzzle game installed on their phone at least for appearance sakes. Although i do find number puzzle games like 2048 rather engaging and great for those moments where you have the need to kill a few moments without looking like a child. The game is simple enough and just requires one to add up number blocks in the multiples of 2 to form higher numbers. Besides 2048, there are other games with similar gameplay like THREES or EIGHTS in the Play Store. If you are a parent, you should probably consider installing this for your kids.
4. BROTHERS IN ARMS 3
This one is another Symbian classic for me, the game has some great graphics, sound effects and great gameplay (although it can be a bit repetitive). The game is littered with the usually gameloft In-app purchases, which could make the game a bit frustrating. However it does make for a challenging game.
5. HITMAN GO.
Hitman GO is a tad unusual especially for fans of the Hitman franchise. Instead of the adventure game you get a puzzle based board game which is good in a way.
Injustice: Gods among us
Batman Arkham origins
Godfire: Rise of Prometheus
Shadow Fight 2
Assassin's Creed Pirates