Finally got the game today… played it for a little bit…
This was my first reaction…
WOAH =O
This game is brilliant in all its forms.
Presentation
You start off with background story (in Japanese) that an Empire is starting to take over your country. You and a friend (I believe the characters are both women here) are put up to the task of leading the resistance force against the Empire. After a quick optional tutorial, which takes 5 seconds to look and comprehend (images help a ton), you are immediately thrown into the battlefield.
Graphics
Some really nice eye candy here, a very realistic view of the battlefield with some amazing attention to the tiny details (more on that later) which makes it look definitely polished.
Sound/Music
Sound effects do their part by providing some realism, particularly with explosions. You get two types of soundtracks to choose from, the original Arcade synth and the Dreamcast exclusive arranged which features live guitar segments in the stage themes. Both soundtracks accompany the action to a tee. Can’t say more on that, it’s perfect. Kudos to Shinji Hosoe for coming out with such a ROCKIN’ soundtrack
Gameplay
The helicopter is a bit difficult to control at first, but you quickly notice which button does what. What’s interesting is that there is a button for options (Machine Gun, Rocket, Cannon, etc…), one for bombs and one to recharge your current option. While it cannot rotate 360 degrees like Zero Gunner 2’s helis, you still get a feel of freedom when moving about.
Attention to detail
This is easily one the best aspects going for it. Right in stage 1, various things interact with the surrounding environement.
Here are a few examples:
There are cows running around on the ground, blow up a tank near them and they keel over in shock 
When you blow up anything, you see huge plumes of smoke into the air and gets blown away if you fly into it.
The first boss appears and mercilessly chops up a flock of birds as it flies towards you with its rotor. It’s a helicopter that’s twice your size and is equipped with machine guns. As you fight it over a swampy area, you see the reflection of the events in the water below. When you finally defeat it (not as easy as I expected it to be), it twirls slightly before crashing into the ground but hops a bit futher and finally crashes into the swamp with a satisfying boom.
Longevity
Under Defeat could be beaten within half an hour by pros, but the game offers so many bonuses you’ll always be coming back for more. Some extras include exclusive galleries that become unlocked when beating certain stages in certain ways. There are replays available after beating the game once. Beating the game the 1st time also unlocks a harder mode, with a different look on the levels.
Fun Factor
Well… do you like blowing stuff up ? In need of unwinding after a stressfull day at work or school ? Then this game may be for you. It’s very satisfying to figure out how to master the enemies’ patterns and outsmarting the huge bosses. This is the game’s main draw afterall… no complex scoring systems or anything, just blow stuff, badass style !! I like that notion
Overall
As you can see, G.Rev really wanted to do something really special for this game. Unless you can’t stand shooters at all, I see no reason not to look it up, even for curiosity alone. Long live the Dreamcast, and God bless G.Rev for creating such a fun and simple game.