First entry in a series of articles written to help the "Powergamer" crowd who wants the best setup for powering through the Mass Effect games.
Mass Effect:
First off, class selection.
The way this game is, the enemies typically have some shielding you need to break, and then you can hit their health. There are some ammo types and some abilities that can harm shields more effectively, but it's more efficient to just dish out a lot of damage period. Also important is your survivability. Soldiers dish out the most damage, have the highest HP, and can equip heavy armor, so we're gonna go with them.
You get 100 skill points, while your squadmates get 80 (though they have less skills than you do.) So, we must decide something first before we allocate those skill points: what weapon will you focus on? Assault Rifles are great for all situations, unlike sniper rifles and shotguns, which are only effective at a certain range, and Assault Rifles have higher attack stat than pistols, so we're gonna go with those.
Another important thing to consider is that if you have an achievement for using an ability a certain number of times or getting a certain number of kills with a weapon, you can actually choose it as a bonus skill, even if the class you choose can't normally use that skill. For a Soldier, the best bonus skill is Warp, hands-down. When it hits an enemy, it will have two effects over the course of several seconds: it will do a small amount of damage over time, and it weakens your enemy's overall defense, so each of your bullets does extra damage. Killing things is the point of the game, so this skill is a must-have for a Soldier.
On that note, the class specialization you get after doing a sidequest can either make you a Commando who does more damage per shot and gives you cooldown reductions on Marksman and Assassination, or a Shock Trooper, which gives you a health bonus and cooldown reductions on defensive skills. Even though you're not gonna be using the Marksman and Assassin abilities because you're using an Assault Rifle, Commando is the way to go. You're already gonna have a ton of defense, so you don't need more defense as much as you need more firepower.
From there, the end build is pretty simple: start out by maxing out every skill except for Pistol, Shotgun, Sniper Rifle, Charm, and Intimidate. After you max out every other skill, you can opt to put a few points in Sniper Rifle, Charm, or Intimidate, doesn't really matter. Early on, you'll want to put a couple of points in a large amount of skills to grab a bunch of abilities, then focus on putting points in Combat Armor until you can equip heavy armor, then focus on Assault Rifle and Fitness. From there, it's up to you.
So now that we have an awesome Commander Shepard set up, we need an awesome squad to match. I recommend Wrex and Garrus. Wrex is a defensive powerhouse, with heavy armor, Barrier, and Immunity, plus he has the ever-useful Warp ability, to supplement your own when yours is on cooldown, and he has an extremely powerful melee attack. Garrus is needed because of his Tech skills, so you can open doors and item containers; Tali can do this as well, but Garrus is more suited for battle than she is. I also recommend Assault Rifles be the weapon your squadmates focus on. As for their skills, just don't put points into weapon skills other than Assault Rifle; for Garrus, don't max his class skill, and for Wrex, only put 1 point into Stasis.
For weapons, just use the best Assault Rifles available. When you're nearing level 60 on a subsequent playthrough, you can buy the best Assault Rifle at C-Sec, and you can buy the shop's license so the quartermaster on your ship will also sometimes sell it, so you can get 3 copies of it. The best armor, in general, is either Predator or Colossus heavy armor. Getting the best items from shops is random and you could actually miss out on getting all the best stuff in a given playthrough, so a trick you can do is complete a major story planet, go to a shop, save before talking to the shopkeeper, then check his stock. If he doesn't have what you want, reload your save and check again, and his stock will be random each time, but after you talk to him is when his stock is "set in stone" as for what it'll have until the next time it's randomized.
Now, upgrades. The best weapons can hold two gun upgrades and an ammo upgrade, and armor can hold two upgrades. For weapons, my favorite setup is Scram Rail X/Frictionless Materials X, with Inferno Rounds X ammo. The Scram Rail raises a weapon's attack power but makes it overheat quicker, but Frictionless Materials give a slight attack boost and lower the rate at which a gun overheats, so you end up with a flat attack bonus and a slight heat reduction. Put this on two members of your squad, but for the third, instead use Scram Rail X/Frictionless Materials X/Polonium Rounds VII. This sets it up so the enemies will have two separate damage over time effects ticking on them at the same time. The Polonium Rounds only go up to rank VII, so make sure to hold onto one copy of them when you get them, because they will stop being spawned when you level up past a certain point and you'll be unable to get any more without creating a whole new character.
For armor, use pretty much whatever looks good. I like to put one copy of Medical Exoskeleton X on Garrus because he doesn't normally have the ability to regen health over time, which is vital, and it also reduces his cooldowns and reduces the poison damage he takes. Energized Plating X and Shield Interface X are good for extra defense. Combat Exoskeleton X is good for raising your melee damage.
Never kill an enemy while inside the Mako vehicle, you get less experience points that way. You can damage enemies while in the Mako, just make sure to exit the vehicle before actually killing the enemy.
As a final note, remember that almost every single story-related decision you make and what sidequests you completed will be carried over to Mass Effect 2 if you import your savefile from the first game, so make sure your final playthrough reflects the decisions you want to carry over. Hitting the level cap, 60, will let you start at a slightly higher level in Mass Effect 2, and having over 100,000 credits and lots of minerals helps a bit when carrying over a save.