For those that have played the travesty that was Iridion 3D, let me assure you that Iridion II is 100% better. Props to Majesco for really turning this series around.
Iridion II is a "3D" vertical space shooter. In this installment, the Iridions are back to take over Earth from the humans again. It is your job to stop them.
To start, there is a training level which helps you with the basics of the game. After that, it is onto your first of 16 missions (in 4 different worlds), each containing huge bosses and mini-bosses.
Your ship has the ability to select from six different weapons of your choice, which can then each be upgraded to improve their power. You can also pick up smart bombs (which destroy all regular enemies on the screen or severely damage bosses) and health units (yup, your ship isn't destroyed in one or two hits ). You can also adjust the position of your side cannons for narrow fire (for vertical lines of enemies) or wider fire (for horizontal rows of enemies).
Each of the 16 levels is varied and consists of your average shooter enemies. Enemy patterns are usually pretty predictable and most enemies are easy to eliminate. However, since a lot of the levels are decently long and usually contain a boss and mini-boss, the game isn't a cake walk. Adjustable difficulty helps novice players and gives experts more of a challenge. There are also unlockable modes where you can take on just the bosses and see how many you can defeat, and how long you can survive.
The graphics are pretty good, with decent attempts at 3D (since the GBA cannot do true 3D). Bosses are unique and cool, and enemy fire is easy to see. The level backgrounds are nice, but a tad repetitive (in each separate level).
The shining aspect of this game is the sound. I loved the music, and an unlockable jukebox option allows you to listen to the music or decide which tunes you want to hear or turn off.
Overall, fans of the shooter genre will enjoy this game. While it not the most unique or challenging game, it certainly is fun and enjoyable, and better than most shooters for the GBA. Don't be discouraged if you played Iridion 3D to pick up this game -- it would take more effort to make Iridion II worse than the original than better.