Only enemy is falling balls. Quartet - A sidescrolling platform shooter that features 4 player simultaneous play, if you can cram everyone at the keyboard. Rampage - A very solid port of Rampage, especially for the time it was released. Robotron - a unique classic shooter. Rolling Thunder - Become a secret agent, infiltrate enemy headquarters, and save the world in this side scrolling platform shooter.
Graphics are a wee bit blocky.
Rygar - One of the more complex sidescrolling platform games to be released at the time. Various types of enemies to encounter and destroy. A very good and playable port. See below links for a url where you can grab a shareware version of one of these emulators.