Robotron: 2084

In Robotron: 2084, you play as humanity's last hope against the Robotron, the robots who made their creators obsolete. You are the only thing preventing your species from going extinct. The story is explained in the game. (before playing)

Wikipedia, because I only use the most accurate sources (that have probably been changed to the point where they aren't): https://en.wikipedia.org/wiki/Robotron:_2084

This is a site: http://www.robotron-2084.co.uk/

I would say go out and buy a copy, but arcade machines usually cost around $2000.

Spoiler

Cave Story and Robotron: 2084 are tied for my all-time favorite game.

 

I think it definitely holds up as one of the better shooty games of the period, if only because it doesn't control like arse. Geez it ramps up quickly though, there's only one level before it's throwing indestructible targets and fast homing kills everywhere. The main thing I don't like is all the bright flashing colours, there are so many rainbows being vomited it's hard to keep track of anything.

A good modern take on the subgenre can be found in the Geometry Wars series, from what I've seen.