ASL's success it based upon one primary factory: Time.
An ASL scenario can be knocked out in easily in a evening's play. A game of 3R takes at least a weekend -- and even then it won't go to completion because one side of the other will quit before the end of 1943. No strategic game of any value can be completed in an evening. Thus, ASL will beat all of them hands down.
ASL isn't a "strategic" game, it's a tactical one, though. I'm not sure that time is really an issue - that all depends on the player, and the scenario, no?
Other tactical games are more successful than ASL -- Warhammer being the best example. Game of equal or perhaps greater following (depends on the year) are Battletech and Star Fleet battles. Tactical games that were good but lacked the neccessary support to get them ASL's level of success were Firepower and Sniper -- both of these were man-to-man and Firepower was doomed from the get to because it was based upon post-WWII combat.
Firepower was based on Close Assault, which was Second World War combat, and Sniper included both - as did Hetzer, the sequel to Sniper. I remember them being quite popular, not doomed. As for ASL's level of success, that's not a realistic yardstick in my opinion. If you have to have 20 modules, a 30 year history, and a 500 page rulebook to be considered a success, that rules out every other game.
ASL does tactical infantry combat well.
Which aspects? Command and control are non-existent, support weapons usage is mostly fantasy, and the amount of sleaze outweighs the number of real life decisions a commander would make - skulking being just one example (how many infantry commanders would deploy to a building, run outside the building, then advance back into the building 30 seconds later?
) The omniscience of the player is another issue - I think Combat Mission on the PC handles these issues much better, due to being a PC game, but of course if you want to scale a wall, swim across a river, ride in a glider, drop by parachute, drive a captured truck, and/or interrogate some civilians it lacks the detailed rules to do all that stuff, which 99.9% of the time no one did anyway.
Squads in battle routinely deployed into fire teams (even if they didn't call them that) but in ASL this tactic is disadvantageous if it separates one from a leader helpful in making a fire attack, or from a "killer stack" in close combat. Perhaps this is a function of the hex scale - is 40 metres really a reasonable space for a squad? So much time has passed since 1977 that to question the core foundations of the game is not heresy, but really pointless - you kind of accept ASL for what it is - a game - and run with it. Reading some of the comments in the thread, it would seem many are convinced ASL has transcended its own intent.