The Chromanoids are invading the solar system. You, the Captain of the human fleet, must take charge and shoot them out of the sky before they arrive. With such a classic premise for an entertaining arcade game, Chromanoids™ [$0.99] starts out great.

The game is loosely based on Missile Command. You have a central weapon at the bottom of the screen, and alien attackers fly at it from all directions. Tap to fire missiles and interrupt them before they destroy you. The trick is in the timing: your missiles take time to reach their destinations and the alien ships are also moving, so without the right amount of lead time the missiles explode harmlessly behind the attackers. The aliens also get trickier as you progress, shielding, swerving and phasing to slip by your defenses.

There's a score of games on the App Store that follow that formula, but Chromanoids™ goes further to differentiate itself. The Chromanoids are all different colors, and your missiles can only hurt matching colors. Below your weapon are three primary color panels. Before launching a missile, you need to tap the correct color to fire. The attackers are quick to adapt, so you'll soon be mixing colors on the fly. It's a twist that makes the game much more challenging and a bit more fresh.

The game has five modes to hold your interest. Story mode gives you 25 waves punctuated with cute dialog cuts. Armada mode is harder and faster. Depleted mode stacks the odds further against you, so your shots are smaller but your score gets higher. Ultradrive mode rewards accuracy. Red-Shift mode does away with the color matching mechanic so you can blast away freely. Chromanoids™ has enough variety to keep any arcade fan happy. And if only Hothead Games had been equally generous with its payment model, I'd completely recommend it.

As a freemium game, Chromanoids™ would be very reasonable. You get 75 credits to start, and it costs 25 credits to continue playing after you use up your first few lives. You earn credits slowly through daily play, or you can buy them at a generous 1000 for $0.99 or 4000 for $1.99 You can also pay for powerups, but you can earn them in regular play.� So if Chromanoids™ were free, it would be an easy recommendation. But it's not, and it's not an easy game, so you're going to need to hit Continue a few times.

Unfortunately, this also makes the Game Center leaderboards sort of meaningless. Since you can pay to keep going without losing your score, there's no way to know if you're competing against people who are skilled or just have deep pockets. Maybe this is an attempt to be super faithful to classic quarter-pumping arcade games?

At least Chromanoids ™ is a good homage to those games in every other way, with stylish retro art, a campy storyline and good sound. If Hothead Games decides to drop it down to free at any point, I'll have an easier time recommending it. You'll probably only ever need to spend an extra buck or two, so if you're fine with that, it's a good buy. But if you're put off by paying for extras in a paid game, you might want to give this one a pass.