Kain there are 3 things which will bring in the punters;
1. Appearance (website and game)
2. Positive Reviews from Reviewers that matter
3. Fun Factor (play the demo and ask yourself, would you actually part with cash for it?)
The latter 2 aren't actually as important as the first one;
Graphics and Presentation literally make or break games...
Although the gameplay might suck, there is just so much emphasis placed on graphics that if there is actually gameplay as well - the game is considered a 'breath of fresh air'.
As this is being sold online; having a site which looks the part is really paramount. You want it to basically suck the players into your game before they've ever had a chance to play it; your trying to hype up the player to actually believe the game is more fun than it actually is (if it is actually awesome then, bonus).
As the aim of the game is to 'hi-jack' from ships then the site's logo should really show this... as it is based in space and on planets again the logo should show this;
Perhaps have the players ship, with a tractor beam on another ship dragging it along; the background could change from a space nebula, to a ground grassy hills look to an asteriod belt.
If you have the players ship as if it is comming towards the player kinda off to the left but angled toward the center slightly; so you see the ship being hi-jacked in the background.
Maybe add to the action appearance by having 2-3ships in the background firing towards the ship; each time the background changes they change to a different type but same position.
This will give people who visit the site a sense that the game is intense; which is what you want them to think, because 50 levels sounds great but this is basically R-Type and after a few levels you know what is going on and it'll only keep the short attention span people.
You want to also have other visual things happening across the site; a menu down the left-hand allowing you to set pages to the right actually has more appeal as it brings attention to the menu so people explore the site; but also you feel like there is a space specifically for the games information rather than it being simply presented to you.
Another thing is on the main page you want something moving; some sort of image that keeps peoples attention;
Flash is very good here, and it could focus on anything... for something like this you'd want a presentation flash with action screenshot with basic overviews of the features of the game.
However you'll want to play down any un-edited screenshots, not created for people to be wow-ed by as the graphics currently are a let down.
Another thing you'll want to do is rework the games graphics a little; rather than a simple snaking laser beam, make it so the laser beam glows and blurs as it wiggles towards the player.
The explosions are nice, but for this type of title you want Jerry Anderson style, multiple OTT explosions as if everything is full of nitrogliserin.
The ships engines should glow and show very visible flame effects; smoke effects too, hinder gameplay but add visually.
As it stands the game is technically good; but right now you need to up the steaks so that Mr. Armchair Gamer will look at it and go 'Woah! that looks intense'
Whether you like it or not games people buy will be compared to other PC and Console titles by high end developers; so the visual appearance really is the sale as far as they're conserned.
A demo for this kind of game should be a basic 3 level thing; enough to meet the first boss and get into the game, but not enough to get bored of it.
GamePlay trailers are a no-no; you want to hype the tension of it, so a game trailer consisting mainly of cut-scenes from the game is more what you want.
A story line for the game, no matter how flimsy but an excuse to add cut-scenes and characters that gamers will get attached to is also a nice twist which people will react to.
If you want game graphics wise, i'd be willing to help you out; try and help you add in that je ne c'est quoi