After using my new build in Orr areas and Far Shiverpeaks I've concluded that I wasn't really playing engineer until now. This build is cure for every single problem of Engineers.
Damage It pulls more damage than any possible combination of weapon set, elixir/flamethrower gun or turret. You will forget that you have weapons at all when you get used to bombs and grenades. Use fast-ground targeting for Grenade Kit. It will feel like hand cannon when you get used to it. I've been thinking that my previous build specialized on kiting and applying condition until now but bomb-grenade kits have access to more condition (only lack fear and weakness) and they can offer wide range of control or kiting opportunity. You will have double chill, blind, cripple, immobilizing skills, endless burn and bleed stacks and 3 fields of poison that will melt your foes in seconds. One single grenade deals 600-700 direct damage and you throw 3 when you take Grenadier skill. In total you will deal around 1800 non-critical damage with just Throw Grenade skill. Now figure how can any of weapon set do that much damage with one shot.
Survival Before going on survival opportunities in this build I have to say that WoW-diseased classic mmo players will suffer while learning the mechanics of Guild Wars 2. We all learning, each day, that something we have been doing in other mmo's is not even an option in Guild Wars 2. I got used to gw2 combat, event system or other primary features quickly in BWE tests but some other things come up at higher levels. Survival stats and gear are one of these things. I haven't played any mmo for 2 years but I instinctively collected damage gear like I will never have problem with staying alive. I think we all do have problem with it. You can't survive just with your dodge and control skills. You have to stack at least one of the toughness, vitality or healing power stats to level up safely. I did that mistake and many people are doing it right now but people will learn soon that survival gear is important. I think people still think that survival gear is for tanks even they do well know there is no tank role. It is a bad habit from classic mmo's.
Engineer should stack toughness as top priority stat for survival. I purchased Knight (Power/Precision
Traits Trait lines are obvious choices. There are few crucial traits for this build rest is optional and you can implement whatever trait fits your playstyle.
Forceful Explosives: Larger explosion radius. It's a must trait. You can't miss your
Elixir-Infused Bombs: Bombs heal allies. And you. Each bomb will heal you 200ish hp and its huge. You will get non-stop healing while bombing large packs.
Grenadier: You throw extra grenade with each grenade skill and range is increased by %25. Technically it's one free skill for every two skill use. Instead of 2 grenades you will throw 3.
We have not much choice in Inventions line. Elixir-Infused Bombs and Reinforced Shield are therefore no brainer traits. First major trait has no directly useful trait. Every option is equally useful to me so it is up to you to choose. I choose Explosive Descent! Just for fun. %50 less fall damage? Hell yea! In Firearms there are Infused Precision which will keep you at constant swiftness boon and Knee Shot which will cripple immobilized targets. I go with first but again it's up to your choice. By the way Steel-Packed Powder (Explosions cause vulnerability) minor trait is overpowered. After a few explosions your targets will be stacked to max vulnerability which means they will take even more damage.
Combat Try not to waste your bombs and grenades less than 3 melee targets. Pack them, control them and bomb the shit out of them. Yesterday I pulled 10+ Svanir mobs in Far Shiverpeak, including ranged, hunter, berserker mobs and they died in a few seconds while I used supply crate, turret and one healing skill to survive. I've completed a dynamic event with one pull. This might not seem important for some classes but it's huge improvement for an Engineer. All Engineers who died countless times in personal story quests will understand my point. I know Engineers have suffered from risen mobs as well as other classes (except warrior) but fear no more. Chill them, apply conditions and then just spam bombs. They will be sorry that they are not dead. Actually they are the reason that encouraged me to try this build so I have to thank them and I do this by sending their souls to rest.
This is overall build for any leveling or PvE damage focused Engineer. I haven't tried it in dungeon yet but I don't think It will fail me. Grenade kit is also best choice for WvW and in underwater combat as well.
Conclusion I must say that I've never seen any engineer using bomb or grenade focused build but there might be some other people who have already leveled all along with similar build. Please have a discussion here and inform us if you have more useful tips. Although I've discovered all of these after hours of experimenting, this build is new to me and it needs more challenges to be proved as reliable.
I must add a few more things about this build apart from its practical advantages. The most important thing about this build is that you will feel like an Engineer! Seriously, running around with ridiculous sounded funny pistols is not the gameplay I expected from an Engineer. I must feel the impact of my guns, I wanna see blasts and booms and I want to see huge numbers floating on my foe's head. Rifle feels like real weapon but again it's a total joke with its control focused low damage skills. But bombs and grenades are completely different. You will feel the explosions, the rumbling of earth, the sounds... You will feel like you are really destroying something. That's what I was expecting before rolling an Engineer. I'm finally glad to have an Engineer main but I regret that I waited until 70 to try out amazing capacity of Engineer.
Have fun this build.
Edit: Grenades do not benefit from Forceful Explosions so you if you are grenade focused then you should change it. It is still very important for bomb focused play. Shield gives toughness when you wield it. Consider changing Reinforced Shield trait if you won't be using shield too much. (Thanks to nanowizard for info)
Edit 2: Knight armor is the closest stats for this build for now. Power/Precision/Toughness