ASL2's complexity doesn't reveal itself until the second mission, when players get to configure their assault suit. You have an immense number of choices, from suit type, weapons, armor, power systems, targeting systems, boosters, shields, and more. There are over 49 different types of weapons alone, and at least 8 different assault suits. Your ability to access each accessory depends on your performance from the previous mission, ensuring that players will replay missions until they've got them perfect.
In essence, what NCS Masaya has created is less of a shooter than a mech sim. This is a hardcore gamer's dream. Each choice you make in choosing your mech is essential. Weapons have ranges, damage ratings, weight, as well as damage types, and each system is logically designed. You can spend hours trying to tweak your assault suit for optimal performance and mission type. For example, you'll want to bone up on force screens for the second mission, otherwise you can pounded to death by the avalanche.
A word to the wise: if you're a novice platformer/shooter player, don't play this game. Like Target Earth, this game is HARD. Possibly harder. Levels are difficult in the extreme, and your allies are pathetically easy to destroy. Unless you're the type of person that doesn't mind dying time and time again until they've got the right mixture of mech design and luck, you'll run out of patience well before the second level. If you've got the skill and guts, though, this game controls and plays like no other.
Although side-scrollers like Sengoku Blade or Hyperduel are definitely flashier, with better graphics and cooler music, their depth is a puddle next to the ocean that is ASL2. NCS Masaya's created a shooter where the player's character is a true individual, with unique capabilities, rather than a sprite with different powerups. It can accommodate different players with differing tactics, something that very few games can, 2D or 3D. A rare feat.