SL (the original game, no expansions) is a much simpler game than ASL, but its scope is much narrower. The "feel" of SL is similar to ASL; i.e., they both play very similarly. However, there are very few rules that are at all the same between the two systems, and many rules are completely different. This can be a problem when jumping from SL to ASL: you have to unlearn a lot of the old before you can start learning the new.

As you add the new rules from the expansion gamettes (Cross of Iron, Crescendo of Doom and GI: Anvil of Victory) on to the basic SL system, the game increases in complexity and difficulty, and becomes closer in scope to ASL. However, the mish-mash of rules created by combining the gamettes makes it an even harder game to learn than ASL (even with Programmed Instruction), and the rules lack a lot of the elegance the ASL rules have (there are a lot of interconnected systems and procedures in ASL).

ASL appears daunting at first, but if you can find an opponent who is prepared to teach you, it's not that hard to get up to speed with all the basic rules; the rest is just detail that becomes easier to remember the more you play. The other comment that ASL is a "lifestyle" is very true in a lot of ways. The "casual" ASL player is unlikely to get very much out of the game; you don't need to play it *exclusively* but if you're not going to play it *regularly* you will have a hard time becoming comfortable with it. (The same is true of SL/COI/COD/GI however.)