Having played the original Dreamcast version years ago, I was pretty happy to hear this was coming to Steam. The end result was worth the wait. The visuals still hold up nicely (especially the smoke and "shockwave" effect of bigger explosions), the music is good with multiple soundtracks to choose from, the controls are crisp and quick to respond to your controller input, and there's a new 16x9 widescreen mode called "New Order" that changes things up a bit in terms of enemies and whatnot. There's also a pretty nice selection of helicopters to choose from on top of the original helicopter, each with its own main weapon system to try out.
As for the game itself, it's a solid "into-the-screen" isometric shmup. With 5 levels to play through, you have several weapons to choose from as you attack enemies in the air and on the ground. These are Vulcan (rapid fire), cannon (slower, but does more damage), and rocket (still slower, but it explodes and does damage over a bigger area). These are on top of the constant weapon your helicopter always has (which is basically twin vulcan guns). You also get bombs to use, which fill the screen with explosions and cause a good bit of damage to air and ground enemies.
The helicopter has an interesting movement setup, in that when you're not firing, it will angle to the left when you move left, or right when you move right. And when you fire, it stays locked at that angle until you stop firing again. This angling can be inverted, so that the helicopter angels in the opposite direction you move (i.e. if you move right, it angles to the left, and vice versa). You also get a perk for not firing constantly in the form of an temporary option that you can spawn, which fires whichever special weapon you have (vulcan, rocket or cannon). As I said, it's temporary though, and it goes away after a short time. And when it's gone, it has to recharge for a bit before you can summon another one. Add in some scoring bonuses here and there (like trying to destroy 100% of the enemies), a hi score online system, an art gallery, and some wallpapers to use when playing the original arcade mode (which is 4x3), and there's a lot to like with this game.
In the end, this is a solid, enjoyable shmup that's well put together (not surprising, since it was done by G.rev). It's also not a cakewalk, even on Easy. And with the extra modes, OSTs, and helicopters, it's got more to offer than the Dreamcast version, or even the PS3/360 re-release. So if you like flying a chopper and blowing up everything that isn't you, I think this game will scratch that itch pretty nicely for you.