The Berserker may be the scrappiest of the classes, but the Engineer is the weightiest. The satisfying arcing thwack of her wrench pulverises pretty much anything that gets in her way. She's the slowest class to play but, due to the high Strength/high Vitality opening stat combo, is also the most resilient. Where the Berserker is reckless, the Engineer is methodical, tanking through the game while using tactical deployments to control the arenas.
That makes her one of the easier classes to play with, but also a more interesting one than the super-spammy Embermage. There are a host of interesting choices to be made, including a varied selection of skill trees that each favour a different weapon set up.
The Engineer's Charge bar is broken down into five segments that activate as she does damage. Unlike the other class bars, the meter doesn't need to be full to make use of it. Instead, certain skills use up one segment to activate more powerful versions of their default attack. Others will drain the entire bar, doing extra damage proportional to the number of segments filled. A big part of what makes the class so tactically diverse is deciding exactly when and how to use it.
For instance, Flame Hammer, the starting Engineer skill and, for once, one worth keeping hold of. It strikes the ground, creating a crater of fire and trailing flaming snakes out from the centre. It's powerful, impressive looking and, when there's Charge available, it generates multiple explosions. It's the best of the early Engineer abilities, and one that's worth upgrading through to the first tier bonus.
The other unlock to prioritise is Healing Bot which, true to name, deploys a little robot that follows you around, periodically casting a pulse that heals both you and your pet. It's not quite good enough to help you out if you're fighting for your life, but as a way to recharge between encounters it's invaluable (and adorable). Once deployed, it stays on the map until you leave the area. Pop the skill in your hotbar and get into the habit of deploying it whenever you enter a new level.
Your big decision when playing as the Engineer is whether to use two-handed weapons or a melee/shield combo. While it's a matter of preference, I'd advise going with the former. The shield specific skill, Shield Bash, is a bit crap. As Torchlight 2 is a 'best defence is a good offence' kind of game, pick up the Heavy Lifting passive instead, which increases the attack speed of two-handed weapons, counteracting their natural sluggishness. Also consider the Charge Domination passive. It gives a small chance to fill your Charge bar when you kill an enemy.
The other Engineer weapon of choice is the cannon. Pop one in your secondary weapon slot and you can switch between it and your melee weapon with the W key. While the cannon isn't the most useful weapon, the Blast Cannon skill is great in certain situations. Plenty of the game's dungeons are full of tight corridors of charging monsters, and the ability's high-damage piercing shot is great for softening up the line before switching back and introducing them to Mr. Hammer.
Finally, an absolute essential upgrade is the level 14 Spider Mines. It allows the Engineer to deploy three robotic spiders that seek out enemies and explode on contact. Why so essential? Because they're exploding robotic spiders! What other reason do you need?