Engineer is different from the ranger because of kits. It can't change weapons mid-combat, but it can equip and switch the bomb kit, flamethrower kit, medic kit, turret kit and grenade kit. All these kits switch out three of your weapon skills, and give you a fourth and fifth skill depending on the weapon/s you have equipped. Main hand: gun, offhand: gun, shield, 2 handed: rifle.
Using all of these tools, the Engineer can do a lot of things. But is there any thing that it can do that a ranger cannot? No. An engineer can tank with it's med-pack and sheild/gun. And engineer can do closequarters combat with it's gun/sheild and bomb kit. An engineer can do mid-range combat with it's flamethrower kit and dual pistols. An engineer can do long range damage with it's rifle and it's grenade kit. An engineer can do crowd control with it's turret kit and rifle.
A ranger can do all of these things, but to do them, A ranger player will have to play completely different from an Engineer. The same is true for EVERY proffession in Guild Wars 2.
People need to understand this.
And yes, I am saying that Eles can tank (with earth attunement and a wand), and Warriors can be long-range (rifle). But each way will be different to play.