The Good: Trials Frontier has excellent physics-based 2D racing. There is a ton of content to explore. New bikes and upgrades keep the game interesting and addictive. The Bad: The Freemium model limits your playtime. The throttle will occasionally stop working for no obvious reason. The Bottom Line: With tons of tracks, unlockable bikes, and several quests, Trials Frontier is a great download for 2D racing fans, but beware the freemium limitations. Trials Frontier is the first time the Trials motocross franchise has come to iOS, but with an enormous amount of content and tight racing gameplay, it's a must have for racing fans.The only problem is you're going to need a little patience. Trials Frontier is a freemium game that limits how much you can play in a sitting. It's one of my least favorite freemium strategies for getting money out of users, but in the case of this game, the wait times are worth it to me.Originally a Java Web browser game all the way back in 2000, Trials has seen many iterations. It finally made it to Windows desktops in 2007, then even had a release on XBox 360 in 2012. But this year it's hitting all the major smartphones and gaming platforms, including this debut on iOS.Controlling your bikeThe game starts you off easy, letting you go through a couple of runs to learn the ropes. As a 2D racer with tight physics-based gameplay, you're not worried about turning corners; instead, you control the throttle with buttons on the right, and have buttons on the left for tilting your bike forward and back.Learning how to control your bike is the key to success in this game because navigating over jumps, up steep hill climbs, and over the game's many obstacles takes precision if you want to go for good times. It's also not always about speed; many of the challenges in the game require you to get a certain number of forward or backflips, so knowing how to tilt your bike just right is mandatory.One problem I found is that sometimes the throttle will turn off inexplicably. It's not a complete showstopper because you can always reset a race, but it can be annoying when you're having a great run and suddenly run out of juice.An insane amount of contentAfter the initial tutorial levels, you'll reach a village that becomes your base camp for the rest of the game. In the village, a saloon acts as the place to get quests from the game's many silly characters, a garage lets you upgrade and build new bikes, and the in-game store lets you spend real money for in-game cash. Your main goal is to chase after an evil rider and his gang of nefarious sidekicks, and vanquish them by beating them on one of more than 70 racetracks.Not only are there an enormous number of tracks, but there are 10 unique environments that include rocky deserts, urban factory settings, and even haunted house-themed levels. You'll be racing them all many times as you complete more than 250 quests with challenges that have you doing specific numbers of flips, popping wheelies, collecting items, and trying to get the most air possible.As I played through this game over the past few days, I was amazed at just how much content there is, so if it's game variation you're looking for, Trials Frontier has it. Upgrading parts and bikesAs you progress, you'll meet new characters in the saloon that will help you find the blueprints for new bikes, and parts to upgrade your current bikes. Each of these require you race through a track to the end, then spin a wheel to win a piece of a blueprint or a bike part. When you fill out an entire blueprint, you can enter the garage to build your new bike.