I agree that this game doesn't have much to offer in terms of graphic, but bare in mind that this game is an old game. The fact that they managed to create such a smooth engine is in itself incredible, but when you take the addictiveness and fun ratio into account, the game scores a five mark. I wish I could give it more.
Silpheed is a space shooter. You fly around and clear a route through enemy infested territory. It is a type of game we know too well today, but it was virtually unheard of in the days the game was released. So, strong marks for originality as well. What strikes me about the game is that, even though you get a fair warning (because of the angle in the game) before an enemy approaches you, the game is very difficult. You really have to do your best to stay alive. Although the best part of the game is picking up power boosts. They might be simple bonus scores, shield enhancers and so on. Another thing that makes this game so great is the ability to custom equip the ship before every mission (after the first one)!
All in all a very nice game to see how it all began. And, boy, did it begin great!