Axelay was and still is a great example of what a fun 2D scrolling-shooter should be.
Don't write it off completely though, because Axelay is still a blast to play. The weaponry on offer is standard fare, but you are able to upgrade it in stages to create more powerful or protective variants. It was also innovative for its time in that you would often be moved to other ships to battle in a kind of primitive 3D style, giving the impression of movement beyond the 2D plane.
The levels on offer have a variety of natural hazards along with the seemingly endless waves of enemy ships and these can make for some frantic gameplay at times.
As with all games of its ilk, Axelay suffers from being repetitive. Even harder difficulty levels are only really churning out the same game, and there's little difference to what you're already used to.
That said, it has aged well, and is worth playing simply because it's one of the better examples of the genre.