Easily one of the best action games on the GBA.
Astro Boy: Omega Factor is a beat em up/shoot em up/platformer game with over 30 levels to complete and 2 kinds of modes: Birth and Rebirth. You'll start the game with Birth and a short tutorial of knowing the responsive controls. You can punch, kick, finger laser and use 3 special attacks that you can do by charging your special meter by defeating enemies and collecting hearts that also refills your health. To avoid contact with enemy attacks, you must use your jets to get away, and best of all, it can be used diagonally to get away from any situation. but time it right though. Punching allows you to do combos and works well(and you can refill your special meter as well by simply punching enemies) but kicking enemies will allow you to knock them far to the other side of the screen and if an enemy you kicked comes in contact with another enemy, they'll be knocked as well, allowing you to do a chain reaction. It's fun to do this because you can take out multiple enemies and finish them off easier, but not all enemies can be knocked out when kicked however. Your last normal move is the finger laser, which will hit multiple enemies in a row since the laser goes through them and is best used from a distance since you can't move(unless in a flying level). When your special meter is filled, you can now do 3 special attacks: Arm Cannon will let him fire a huge laser from his arm, hit multiple enemies and destroy enemy projectiles, easily the most useful special attack, the EX Dash can be used diagonally and lets him dash into enemies to even go through them to hit more enemies at once with his jets while doing a powerful punch, useful to do damage and avoid enemy attacks, and best of all, the Machine Gun will let him use 2 guns from his behind and shoot all enemies on screen, freeze them until your done using it and destroy enemy projectiles, this is best used to get out of tough situations as well.
The combat in this game is very fast paced, fun and intense. The variety in enemies will force you to use different tactics when facing groups of them, and figuring out what's the best tactics is part of the fun. Enemies will also vary in size from tiny to medium sized to even being huge and taking over 20% of the screen, and their sizes will force you to think what's best to use against them. Numerous levels also have boss levels and they rarely disappoint, each boss is different and can put up a fight on harder difficulties. There's Easy, Normal and Hard, so anyone can beat this game. On Easy you start with 30 for your special meter and can go up to 99 plus there's less enemies to kill, Normal lets you use up to 5 special attacks and Hard only goes up to 3 specials, there's more enemies and obstacles, bosses have more health, new attacks and can be difficult to beat. Hard mode is for the hardcore(and old school gamers). There's always a checkpoint when you go from one level to the next, though on Hard you have to complete a few more levels to reach a checkpoint.
There are technically 3 types of levels(not counting boss levels since they fall into beat em levels): Beat em up levels, flying levels and platforming levels. All are fun in their own ways, and the beat em up levels show up the most. The flying levels are mainly the shoot em up levels having you dodging many enemy projectiles and taking on various things from attacking multiple enemies to dodging random obstacles. The platforming levels allow you to explore more in some sections to find hidden characters, dodge obstacles, and sometimes you don't do much action at all(there's at least 1 level that you won't kill anything in). Some characters can be found in the open, others will force you to break obstacles like walls, etc. to upgrade Astro Boy.
As you progress from each level, you'll meet new characters. After talking to them, you can upgrade Astro Boy. There's 6 parts to upgrade: Life, Punch, Laser, Shot, Jets and Sensor. You can upgrade Life, Punch, Laser and Shot 7 times, Jets 6 times and Sensor 4 times. Life gives you more health and you can take more damage, Punch lets you do more damage with punches and kicks, Laser lets you do more damage with finger laser and Arm Cannon, Shot lets you do more damage with Machine Gun, Jets allow you to dodge more enemy attacks and increases the time used with EX Dash, and Sensor lets you detect hidden characters to find them better. Upgrading Astro after finding characters and engaging in lots of action feels rewarding since you sense him being stronger, and it's essential to do it.
After beating the game in Birth, you can do Rebirth, where you must complete all the levels again, but with a twist: You'll be able to meet new characters you never met before, unlock more characters, most levels have enemies in spots they weren't in at 1st, making it feel different when encountering them, some enemies get replaced with other enemies in certain levels, and you must find all the characters to unlock more and new levels that you couldn't access to at Birth(only in Rebirth) to see the real/true ending after beating over 40 levels. This gives the game some replay value and another reason to play it more. There's also a level select in Rebirth only, and you can replay levels to get high scores and see how fast you can beat levels in the fastest time possible if you want to.
The graphics are among the best on GBA. There's a lot of detail put into characters and even the backgrounds, it's very colorful and a sight to behold. However, 2 things bring it down: Huge pixelated enemies and slowdown. The huge bosses don't look bad, but the numerous huge enemies you fight look a bit distorting, and isn't very good, though it's minor. But slowdown is a problem. On certain flying levels, they'll be too many enemies or enemy projectiles on the screen, slowing the game down a bit. It doesn't happen a lot, but it's there and is considered a flaw. Still a great looking game though.
What's flawless is the sound. The music in this game is upbeat, catchy and never dull, each music you hear matches the levels perfectly. The sound isn't bad at all as the sound effects do their jobs for the most part. Honestly, there's nothing wrong with the sound.
Overall, Astro Boy: Omega Factor is a superb game. It's too short, has huge pixelated enemies and slowdown, but if you can forgive those flaws, this game is worth your time and money. It's one of the most overlooked games because 1.Didn't sell well for it's time, 2.It's based off an unfamiliar anime, and most anime games aren't that good, and 3. It looks like a kiddy game. Don't be fooled by it's looks and the box cover, play this game, it's fun, intense, fast paced and addictive. Final score is 9.0/10.