Mass Effect’s combat is that of a third-person shooter. You control Shepard, and the A.I. controls her/his two squadmates. At the beginning of the game, you can set the difficulty level: Casual, Normal, Veteran, Hardcore or Insanity; Hardcore unlocks upon finishing the game on Normal, and Insanity unlocks upon finishing it on Hardcore. You can choose to let the A.I. control all the squadmates’ abilities, their defensive abilities only, or micromanage all their abilities while they only auto-attack. It’s also possible to switch weapons on the fly, in order to adapt to the enemies’ positioning, and zoom in for more precise targeting (necessary with sniper rifles). There are separate combat menus for weapons and abilities. Each squadmate is equipped with a full array of weapons, even ones their class isn’t proficient with, which is odd. I mean, there’s no situation in which Tali would be helpful with a sniper rifle, for example, so why have her carry one? As for abilities, each one has its own recharge timer, which you can reduce by levelling it up. The same goes for the power and accuracy of a weapon. You can also hotkey abilities, and one key is already assigned to dispensing medigel to recover health.
As mentioned previously, Shepard is the only character able to use grenades and revive fallen squadmates. Normally, if a squadmate goes down, they’ll get back up on their own once all enemies are dead, but Shepard can also bring them back up while combat’s still ongoing, either with the Unity ability from Spectre Training, or simply with medigel, if specialising as a Medic (i.e. Engineer or Sentinel). If Shepard goes down, however, it’s an automatic Critical Mission Failure (or Game Over).
Combat takes place in real time. Shepard can take cover from enemy fire by standing or crouching behind walls, panels or debris. S/he can also sprint for short bursts and pistol-whip enemies that get too close. You can also use the directional arrows to direct the squadmates: Up will send them to the targeted location (usually behind cover), Down will make them stand still, Right will make them focus fire on the targeted enemy, and Left will make them rally to Shepard’s position and follow her/him.
Enemy HP appears as a red bar at the top of the screen alongside the enemy’s name, with some blue blocks in front of it to indicate the state of their kinetic shields, which you need to strip before getting started on their HP. The same applies to the party: you’ll see the lineup displayed at the bottom left of your screen, with red bars for health and blue blocks for shields. Above this, you’ll find the heat gauge for Shepard’s weapon. Each weapon generates different amounts of heat upon being fired (shotguns and sniper rifles being the worst offenders), so if Shepard fires too many shots in a row, her/his weapon may overheat, which will set off a beeping warning and make the weapon unusable for a short while. Weapons can also be overheated with the Sabotage tech skill.
Weapons and armour can be upgraded with attachments. Each weapon can take one upgrade (two for higher-tier models) and another one to its ammo. This covers things like reduced heat generation or increased power, while ammo can be elemental (poison, fire or ice) or just more powerful. Each suit of armour can also take one upgrade (two for high-tier models), with options like health regeneration, increased shields, durability, biotic protection, etc. Grenades can also take one upgrade. Another interesting possibility is that you can turn armour, weapons or upgrades you don’t need into omni-gel, instead of simply selling them. Omni-gel is used for bypassing locks that you fail to open, as well as repairing the Mako, the buggy that serves as the party’s main means of groundside transportation.
Enemies don’t respawn, which means that EXP is in limited supply. The Mako further complicates things. It has shields, a pair of mounted machine guns and a cannon, and is therefore combat-capable, with the added perk of not being affected by atmospheric hazards. It also has rocket boosters for short distance jumps. However, killing enemies with it gains you less EXP than killing them on foot (50% on Normal and 40% on harder difficulties). So the best policy is to use it to soften up serious threats, then get out to finish them off. The Mako is actually the best means of dealing with thresher maws: gigantic worm-like creatures that pop out of the ground when you drive into their nests (circular stretches of flat terrain surrounded by hills). Threshers are worth a hefty load of EXP, but they’re the most dangerous enemies in the game. They spit acid from a distance and try to flatten the party if they get too close. Both moves are lethal, but if you stay in the Mako at a safe distance, you can jump over the acid jets and whittle down their HP until you can finish them off on foot. The acid can damage the Mako, but not as much as it would your characters (it can one-shot squishier folks like Tali or Kaidan).
A diagram of the Mako appears next to the party lineup onscreen while driving, with blue stripes to indicate the state of its shields and damaged sections lighting up in red. You’ll also get visual cues, like sparks, smoke and, eventually, fire. You can fix the Mako with omni-gel, but this will leave it vulnerable and can take a while, if the damage is extensive.
While combat is shooter-based, character development is RPG-based. Each character and class has several talent trees that they can put points in, unlocking new abilities along the way. Shepard can put two points in the abilities of her/his choice upon creation, then gains a total of 100 points over the course of the game: three per level for the first five levels, then two per level until level 35, and finally one per level until level 60. The squadmates gain a total of 80 points over the course of the game: two per level for the first 20 levels, then one per level until level 60. This is justified by the fact that they have fewer talent trees, whereas Shepard even gains an additional one upon becoming a Spectre. Each class has an eponymous, class-specific talent tree, which capitalises on its strengths (e.g. damage and accuracy for a Soldier). For Shepard, this will be replaced by her/his chosen specialisation at level 20, and all points spent prior to the change will carry over.
There’s a New Game+ system, allowing replays with the same character. This is mostly useful if you want the achievement for reaching level 60. The first time you play, the characters are capped at level 50, but finishing the game once will unlock the level 60 cap and increase all EXP rewards by 10% if you actually reached level 50 on your first playthrough. You then need to start a New Game+ with the same Shepard, who will start at level 50 or whatever level you finished your first playthrough at, to have any hopes of hitting level 60, even factoring in the two DLCs. This is actually rather annoying, as if you were being forced to try out the New Game+ system. The only benefit of doing this–apart from getting an achievement–is that you’ll be able to start ME2 at a higher level.
That being said, achievements in this game aren’t just there to look pretty. Some of them grant Shepard bonuses, such as increased weapon damage or EXP gains on subsequent playthroughs. The “Ally” achievements, obtained for spending most of the game with the same squadmates (meaning you would need three playthroughs with three different squadmate combinations to obtain them all), each grant Shepard a bonus characteristic of the corresponding squadmate. E.g. Krogan Ally grants HP regeneration, regardless of Shepard’s class. Moreover, there are also achievements for using each biotic and tech talent a certain number of times, as well as accumulating a certain number of kills with each type of weapon (this also means three playthroughs, each as one of the basic classes). These then become available as bonus talents for Shepard to pick from during the character creation sequence. While this improves versatility (e.g. you could train your Vanguard with sniper rifles, thus giving them a long range option), it also gives you an extra talent tree to manage, which can result in spreading yourself too thin, depending on your Shepard’s chosen build. It can also result in incongruities, such as giving a biotic skill to a non-biotic class, which just doesn’t work lore-wise.