Booster Trooper is best described as a side scrolling shooter. It features both single-player (versus bots) and online multi-player. It has 23 maps, 11 weapons, and 4 game modes: Deathmatch, Team Deathmatch, Capture The Flag, and Destroy The Beacon.
The first few hours have a degree of intrigue as you explore the various maps, game modes, and weapons. After that you discover the game is the same thing over and over regardless of what options and modes you select. The online multi-player was the best feature of the game, but has been dead for quite awhile (unless you can set up a session with friends). Sadly one of the other redeeming features are the achievements. Of course the developers even managed to mess those up as a few have incorrect descriptions/don't unlock properly.
Overall I find it hard to recommend this game even for $1 to $2 (which it commonly goes on sale for). Only buy this game if you're committed to the achievements and can find some friends to play with.
Which is being very generous considering the only positives are multi-player (which is dead) and achievements.
$4.99 on Steam