Humans joined the galactic community after discovering a Prothean data cache on Mars in 2148. Their devotion to understanding and adapting to modern warfare left the staid Councilraces stunned. Humanity's persistence and unflappable spirit has taken them further than anyone in the galaxy could have imagined.
Human engineers are support specialists that set up ambushes, provide fire support, and destroy enemy tech. Their value is not lost on an ally when a battlefield is cleared of turrets.
The Combat Drone is useful for its ability to draw fire away from teammates (even if only for a brief period) and causing a little stress in the enemies' ranks, even on Gold/Platinum difficulties. If there is nothing to target or it's the end of a wave, the drone is the sort of power you might as well use since it will move toward enemies and your power cooldowns will finish before the next wave of enemies arrive.
The Human Engineer has lower shields than other Engineers, so the Combat Drone is a valuable distraction to draw enemy fire away.
At lower difficulties, keep in mind the role you want the drone to have on the battlefield: damage or distraction. With the Rocket upgrade (Rank 6), your drone will deal heavy damage at range; however, it will always back away from the target, making it much less effective at distraction. However, the drone may frequently try to shoot rockets through walls, making this less useful in multiplayer.
For Gold/Platinum difficulties, anything other than a Detonate-evolved drone may prove to be of limited use, due to immense enemy damage and health. Detonate is also the only way a drone can set off power combos, and this can be a useful way to both temporarily distract and severely damage powerful enemies (Geth Primes, Atlases, etc).
On the other hand, it may be wise to skip Combat Drone altogether to focus on maxing the Overload, Incinerate, Fitness, and Alliance Training powers. By doing this, one can get 20% extra weapon damage, and 35% power damage, as well as a few extra capacity points. This tactic allows Incinerate to devastate armour and health, while Overload fills in the gap of dealing with shields and barriers. Combined together, a Human Engineer can be very versatile and capable of taking on almost any enemy single-handedly.
Because Engineers are a power-focused class, one should keep their loadout as light as possible. At 200% recharge speed, you can potentially fire off Overload and Incinerate every 2 seconds, causing utter havoc against enemies of any kind. A good weapon combination to equip is a Carnifex and either a Disciple or Hornet. This combination with power damage and capacity maxed out, gives 160-165% recharge speed or even 200% when using the "Weapon Weight" rank 6 evolution in Alliance Training. Then outfit the Piercing and Barrel mods with the Carnifex, and you can eliminate the Engineer's biggest problem: armor-plated Reaper enemies, or Cerberus Guardians. Combine the powers with this and you have a character with pretty much all bases covered.
If you prefer an assault rifle, the Geth Pulse Rifle and M-8 Avenger at level X are both light enough to give the Human Engineer a 200% recharge speed if the rank 4 "Damage & Capacity" evolution in Alliance Training is chosen.
When equipped with Disruptor Rounds, the Human Engineer can spam a barrage of tech bursts by simply shooting the enemies before unleashing Overload (or vice versa).
An additional option the Human Engineer has is to become a full support character. By evolving Alliance Training for cooldown, Fitness for durability and both Overload and Combat Drone for stunning, you can rapidly volley multiple shocks into groups of targets, keeping many enemies stunned and taking continuous, low damage attacks. Pairing up with other characters with tech powers makes for a potentially very powerful set-up, allowing for continuous creation of tech explosions.
When dealing with a Guardian, release a Combat Drone behind him. The Guardian will turn towards the new threat, showing his sensitive side to your sights. Should you have the Neural Shock evolution of Overload, unleash it on the distracted Guardian to make him drop his shield.
High levels of Overload can wipe out Phantom barriers quickly, making them much easier to take out. If they are doing acrobatics, wait for them to stop before you fire an Overload on them; otherwise it will do less damage.
A weapon equipped with a Piercing Mod is recommended so that you can take on Guardians regardless of their shields, and deal more damage to Atlases and Dragoons alike.
Since the Combat Drone appears behind an enemy, it is best used against Scions to distract them and make them turn around, exposing their back, which is a confirmed weak spot of the enemy.
Because Overload is more effective against barriers, the Human Engineer is very proficient at taking down possessed enemies, along with Praetorians and Collector Captains barriers.
With the recent update, death is not required to trigger Fire Explosions, so the Engineer can be useful for crowd control.
The only risk involving using this character is that the Engineer has no close quarters abilities, so equipping a light shotgun, like the Disciple (which has a useful staggering effect) would be a good choice.
Overload is indispensable against geth troops as all foes other than the basic Geth Trooper have shields, and many geth (being synthetics) take full damage from Overload otherwise. Geth Troopers and man-sized geth that have had their shields removed can also be stunned for a short while.
Overload or Incinerate on a Geth Pyro with a damaged tank will detonate the tank immediately.
Overload followed by Incinerate will devastate shielding via a tech burst: this is a deadly combo when used on Geth Primes since a single burst can strip most of a Prime's shields in one go, even on Gold. This is also a great combo for Pyros: there is a good chance of their exploding by fire explosion, tech burst or tank explosion.
Because most enemies are armored or have only health, Incinerate is extremely useful here. Overload can expose Banshees and Marauders to a burning from Incinerate. All in all, this can be a Human Engineer's best enemy to engage due to the enemies' weakness to Incinerate.
Combat Drones are exceptionally useful at halting the advance of Brutes and Banshees. If one is destroyed, simply deploy another and the enemy will continue trying to fight it rather than you.
The rank 4 evolution Incineration Blast is very useful against the groups of Cannibals that frequently gather to devour their fallen comrades.