NOTE: The spoilers tag is being used to hide elaboration, not actual spoilers.

Front Mission is a mecha-centered turn-based tactics series set in the near-ish future, with battles playing out in various grid-based maps between player and enemy 'Wanzers' (mechs); missions usually focus on defeating all of the enemy forces. Additionally, units and wanzers lost in combat are not permanently lost, at least not that I've ever noticed.

Regarding combat, units in the Front Mission series are broken into 4 (5 in the case of FM3) damageable parts, the left and right arms, legs, and core (pilot as well in FM3), with each part serving particular functions. (SPOILER)The arms hold weapons and shields, and destroying them prevents a unit from attacking or defending; the legs determine unit movement rate and ability to climb terrain, and destroying them prevents a unit from moving more than 1 space a turn; the core holds the pilot and provides energy for the rest of the mech, so destroying it destroys the Wanzer itself; and, in FM3, the pilot controls the Wanzer and can be killed either within the machine or forcefully ejected from it and killed to steal the machine.

From these parts the series gets what sets it apart from most other tbts: the degree of customization open to the player. Various weapon manufactures have developed their own Wanzers, each offering different strengths and weaknesses, communicated through HP value, armor (in some games), weight, and either energy output, movement rate and type, or damage/accuracy. Using these stats, the player is free to mix-and-match said parts to customize their Wanzers to meet the needs of their units.(SPOILER) Generally speaking, the more ideal that last stat (acc, move, ect.), the more the part will weigh, the lower its armor will be, and the less health it will have. So in creating an ideal 'sniper' unit, for instance, a player would want a very high accuracy arm on one side, then a low accuracy arm opposite it to lower weight and to soak up damage for the unit.

Alongside the Wanzer customization, there are also many weapon types for the player to choose to specialize in (though most pilots have a preferred class it is best to leave them with), but they generally break down into three categories: short, mid, and long range, each with specific advantages and disadvantages.(SPOILER) Short range weapons require an adjacent enemy to use, only attack once, and go second to mid class weapons in most games, but are highly accurate and deal extreme damage. Mid range weapons have the most variety to them and are the most task specialized, but their defining trait as a whole is the ability to attack and counter-attack non adjacent enemies. Long ranged weapons are accurate and deal either AoE or high single target damage from far away, but cannot counter attack and are limited by ammunition, often requiring extra ammunition to be stored in a backpack for them.

On top of these basic rules, which are present in (basically) all of the games, Action Point costs were added to the series early on, which all actions consume, and limit a player's ability to move, attack, and counter-attack with certain weapons. (SPOILER)Short ranged weapons have a low AP cost, so they can move, attack, and counter-attack with relative impunity. Mid-ranged weapons have relevant AP costs and often have to select a single attack they'd like to counter on a turn. Long-ranged weapons consume such large amounts of AP they are limited on how far they can move if they want to fire on the same turn.

Alongside weapons, Wanzers have access to shields and backpacks as well. In the case of the former, they operate differently depending on the game in question (being ungodly powerful in FM3 and stupefyingly useless in FM1), but generally they have a low AP cost, reduce incoming damage, and direct said damage to a single part; they are ideal on a damage-soak arm. Backpacks offer utility to a Wanzer, providing additional power for heavier parts, holding extra items, healing allies, spotting for long-range units, ect. They range from costing no AP to fair amounts of it, depending on function.

Moving beyond Wanzer-based customization, there is pilot specialization as well, and pilots gain skill with weapons as they use them, as well as abilities that improve their survivability and damage potential. How these skills are learned varies from game to game, but they (and your brain) are almost exclusively what gives your team the edge in combat, as you are almost always outnumbered.

Regarding what game is the best to start with, I would probably recommend Front Mission 3 or 4. Both had releases in English, offer two stories (though they deal with this in different ways), and require little knowledge of the universe to get the most from. (SPOILER)An enhanced version of the first game is available on the DS, and it is still an excellent title I happily recommend, but the combat is less engaging than later entries. The second game is fantastic as well, but requires the application of a fan-translation to play in English and there are delays in combat that can get annoying. The fifth game, mechanically speaking, is the best of the bunch, but it also requires patching and benefits from an understanding of the universe to get the most out of.