Scale is the first difference between the games. Firepower is man to man while Squad Leader uses small units (with some individual counters for leaders, etc.) Each game has a setting as well. Squad Leader set out to cover nearly any small unit European Theater action from World War II (and never completed the process until ASL came about.) Firepower focuses on post-WWII conflicts and small, quick skirmish actions. (BTW Close Assault from Yaquinto is a WWII version of Firepower.)

Firepower uses an interesting initiative system that was based on SLA Marshall's writings on the performance of men it battle. This makes it a fun game as well as an interesting (if not somewhat controversial) simulation game. If you are interested in modern, small unit actions, Firepower is definitely worth checking out. The rules start out simple but the level of detail that can be added will cover just about anything you might expect to happen in a firefight!

Squad Leader is, of course, a classic. If you want to get the whole package at once, Multi-Man Publishing (www.advanced squad leader.com) was offering all four modules for $60 recently.