I like Point Blank, really fun game that one - and even if you went for a different theme altogether, it's worth noting for any bonus games you care to add. Like firing range shooting targets like in Robocop.
Myself, well I can't help but bring up Operation Wolf. Firstly, the gun wasn't a light gun as far as I know - it was aimed using potentiometers, so had this sturdy UZI rather than a lightgun on a lead. One benefit in that, is there's no need for a screen flash or anything like that. Also, the arcade cabinets were really sturdy - it tended not to be the Op Wolf cabinets that would end up vandalised, someone trying to steal the light gun - the OP Wolf cab could take a beating. I'm mentioning that because it seems like a big part of the nostalgia for me - when you played Op Wolf you did feel like that was a real gun, even as restricted as it was, it felt heavy and dangerous.
The game itself is a lot of fun, often unfair, but always exciting. You should certainly try it, or watch some youtube videos of it - and see how the enemies are handled in that - it'll be pure inspiration. There are enemies that run back and fourth, ones that jump out at you, ones that have a hostages, or appear at a window... there's even nurses walking round during all that - so lots of relevant examples that would help anyone making a 2D rail shooter.
Having static, scroll left, or scroll right levels might be the easiest way - if you want to expand on visuals, maybe consider having a parallax backdrop - like hills then mountains then the sky, all scrolling at more and more reduced speeds.
Always, always have friendlies in amongst the enemies - otherwise theres no risk, and no real need to worry about aiming. If you can somehow save a life, then that's a great way to allow extra lives as well - save a life, earn a life... it's only fair.
Just an idea, but if I was making a side scrolling rail shooter - I'd make a level with no enemies first, then play it, pretending to shoot enemies, and record the position of my shots. Then, I'd go back and add the enemies. The end result would be a level that flows perfectly. Without doing that, I'd be concerned about the game being unfair, or unbalanced - ideally a great player should be able to 100% the enemies, if the game is intuitive then people will appreciate it more I think - like designing a level that way might make the player think they have some godlike ability to predict where the next enemy is coming from - while actually they are just following your predefined instincts.

I got a fever, and the only prescription, is more memes.
