In the AES version, you can continue indefinitely from the level you reached.
Among the arcade machines we got for the Playdead Housewarming party was a machine with Aero Fighters 2 on it. I never tried it before, and played through the first 8 levels with Søren. A cool top-down shooter with great graphics, albeit with a bit of slowdown in certain explody scenes. I should have played a bit more, turns out the game has 10 levels. Anyway, it'll be fun to play it again sometime.
Up until level 10, this game unlimited continues and immediate resume, reseting weapon level, but level 10 changes structure to checkpointing at the beginning of the level. Not quite as mean as Shinobi, but it has the problem of the first 9 levels being trivial given infinite credits, and nothing really preparing you for the challenge of level 10.
Argh! I just rage-shook my controller too hard and accidentally hit the Escape key on the keyboard and quit the game. Now I have to start over .... Dammit.
The city background graphics is superb. It's incredibly detailed and full of personality.
I played through a bunch of the AES version of this game on Easy difficulty. I was doing well, and was sad when the music suddenly hung. This is a known issue in the MiSTer forums, and the cause seems to be unknown. It's a little disappointing.
The last boss fight is a monkey in a UFO, and it's pretty diffiult, even on Easy mode.