Engineer Guide (Mass Effect 2)

Engineer is a magician in Mass Effect 2 as much as Adept which means rather than shooting enemies he will distract and eliminate them using his powers. Having a good set of crowd control and damage-dealing powers it's a very interesting choice to make.

Overview
Engineer has to rely on his powers more than his guns (SMGs and Heavy Pistols) to get the job done. He doesn't have as good crowd control as Adept and doesn't have quickly recharging damage-dealing powers like Pull and Throw used together which means most of the combat time has to be spent in hiding and enemies should be kept at medium to long distance. Finding a sweet safe spot and launching one Incinerate or Overload after another from its cover is the most common tactics for Engineer in combat in ME2.

Powers
There are two kinds of Engineers in the game, Demolishers and Mechanics. Demolisher will concentrate on dealing damage while Mechanic will be more oriented on tricks and distraction. Demolisher is a much stronger character but Mechanic is also fun to play time to time, especially in Geth missions so retraining character for those is an excellent idea to break the Demolisher routine.

Demolisher
Overload and Incinerate are bread and butter for a Demolisher. Overload deals with synthetic and shielded targets while Incinerate burns through armor and flesh. Maximizing skill in both along with Demolisher specialization and faster recharge times and tech damage research will create a true technical battlemage of Mass Effect 2. Basic investment into Drone or Cryo Blast to distract enemies and be able to escape a tough spot still is advised.

Mechanic
Mechanic is a bit weaker choice, especially weak on higher difficulties. This guy specializes in manipulation and tricks to make enemies vunlerable to his and his companions' attacks. He will mostly rely on his fast-recharging Drone ability that allows him to distract a selected enemy and make him stop firing at the squad for a few seconds. Another trick up this guy's sleeve will be AI Hacking and turning enemy robots against him. Finally Cryo Blast will be used to freeze selected enemies so companions can shoot them. For a brave mechanic, Cryo Blast can also serve as a way of advancing some ground, freezing an opponent and than shattering him with melee attack is an excellent strategy. In most cases though Cryo and Drone will be used to cover Mechanic's fall back to a more secure position. Basic investment into Overload and Incinerate is still advised to deal with shielded and armored enemies.

Notable Bonus Powers
With Overload and Incinerate dealing with shields and armor, the only protection type an Engineer can't deal with is Biotic Barrier. This means taking Warp ammo and using SMG to bring down Barriers is strongly advised for all Engineer builds. Picking team version of Warp Ammo will allow to deal with Harbinger and other protected enemies, especially on higher difficulty levels much easier.

Squad Members and required abilities
Due to lack of ability to deal with Barriers, companions with maximized Warp skill like Miranda or Thane will be very valuable assets for a team led by an Engineer. Mechanics with levelled up Cryo Blast will like Grunt a lot since he often charges close-by enemies with his melee attack, incinerating ammo and Krogan shotgun and a well aimed Cryo strike in advance of his charge can allow him to thin enemy ranks very fast. Not to mention his inherent abilities to be team's damage sponge, tank and damage dealer. Jack is also an interesting choice with her Warp Ammo (especially team version) and Shockwave.

All technical companions are redundant at best and shouldn't be picked outside of very specific tech-oriented missions where synthetics will be the main opponent.

Recommended builds
Demolisher:

Heavy Overload 4

Heavy Incinerate 4

Combat Drone 2

Cryo Blast 2

Tech Master 4 -> Demolisher

Team Warp Ammo 4

Mechanic:

Combat Drone 4

Cryo Blast 4

Overload 2

Incinerate 2

AI Hacking 4 -> Improved AI Hacking (robots aren't clustered often enough to warrant mass hacking)

Warp Ammo 4

Weapons and Equipment
Engineers get unique discount when researching equipment so upgrading is very easy.

If Miranda and Thane are chosen to be the companions for their Heavy Warp skill, upgrading SMG to maximum and getting stronger version of it from Tali's recruitment mission is a very cheap and easy route to bring squad's damage up pretty fast.

It's also crucial to get all the techs that reduce cooldown of Engineer abilities since all of them except for Cryo Blast are on a very long in combat conditions 6s cycle. Tech damage is a no-brainer. To strengthen biotic allies, Biotic damage and cooldown upgrades also can't be neglected.

Finally if Grunt joins the team to charge at frozen enemies, it's required to get him a better shotgun or assault rifle as well as upgrade his vitality.