It would not be wrong to say that Apple has given the mobile gaming industry a square kick in the tender regions. From bite-size puzzle games to old-school arcade remakes and even epically long RPGs, we've watched the iPhone morph into a legitimate portable gaming system. When it comes to portable games, iPhone has been building up a lot of momentum in the gaming industry as the mobile platform amasses an impressive growing library of titles.
Below given is the list of top 5 games:
Zen Bound:

Zen Bound is a classy game which everyone should try. It very casual and simple game which reminds you of your old-schools arcade games. In this game you have to manipulate your iPhone to tie a rope around a carved wooden object. Zen Bound displays amazing graphics, art style and more creativity. As per global users it is more relaxing than a yoga session.
Ronaldo:

Every great gaming console has an iconic figure, like Mario on Nintendo, Sonic on Genesis and Ronaldo on iPhone. Ronaldo is a puzzle-based adventure game which will ensure that the smile does not fades away from your face. Everything about Rolando is finely tuned to equal gaming bliss. This game has amazing animations that it won’t let you keep your phone down as the challenge to clear next level keeps your spirit high.
Grand Auto Theft:

Chinatown Wars: This game has proved many people wrong who used to think that iPhone was only good for playing mini games. Grand Theft Auto developed by Rockstar Games give you virtual controls and on-screen buttons so that you do not find it difficult to play. It is a story game with original narrative and creative missions with an option of shooting pedestrians on their face. Grand Theft Auto: Chinatown Wars will make you a believer in serious gaming on the iPhone.
Beneath A Steel Sky-Remastered:

Beneath A Steel Sky is an ultimate point-and-click adventure game. It takes your playing experience to whole new level as it offers loads of new polished features. For just $4.99 you not only experience a fantastic game, but also make perfect use of iPhone’s cutting-edge control schemes.
N.O.V.A.:
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When you are away from your Xbox 360 or PLAYSTATION 3 and are just craving for an arcade game, First Person Shooter action game comes to your mind. iPhone has come up with N.O.V.A. an awesome video game with ultimate graphics. If you compare Gameloft’s N.O.V.A. with any other shooter game, then there is really no contest. The game offers you with excellent pacing, great scenes and most important excellent controls. The game gives you an advantage of multi-player option where you can meet other players to for online death-match action.