Well, it does get tiresome after a while but it's eased by the fact that a lot of them are actually good shooters. For every ten games like Galaga '90, Blazing Lazers, and Gradius II, there were some lame ones like Deep Blue. So, it's a good ratio.
But then again, saying that the Turbo Grafx/PC Engine had a lot of shooters is like saying that the Atari 2600 has a lot of space games.......