"Perception is your environmental awareness and "sixth sense," and affects weapon accuracy in V.A.T.S."
The main draw of Perception (save from the wonderful perks it allows you to access) is the V.A.T.S. accuracy it gives you. So how does this fare? Well, even with a whopping six point investment (going from the mandatory Locksmith perk accessible with Perception 4 to max Perception) you'll see a slight increase in V.A.T.S. accuracy at best. You won't be making long range head-shots with a short-barrel rifle regularly with this investment - heck, even mid-range accuracy is only increased a few percentage points. Of course, the exact increase depends on your range, target and weapon, but don't expect a massive improvement in your accuracy. A welcome increase at short and mid ranges? Sure. But not worth perk investment in itself. Once again, it's all about the perks, just like most other SPECIAL attributes.
This perks allows you to pick pockets more easily. What fun. This is rarely useful, as instead if save/loading and filching mundane loot from foes, you can just you know, go clear out another Raider den? Honestly, the only reason you'll want to get this perk is if you care to score the "Prankster's Return" trophy/achievement. Save up some perks, buy it, get the trophy/achievement, then reload to get your perks back.
Non-automatic rifles are an absolutely wonderful set of weapons that do good damage, often have common, cheap, easily obtainable ammo. You'll find them at all levels, and different weapons that fall under this category can be modded to serve a variety of roles. Need a short-ranged guns? Combat Shotgun works well. Mid-range weapon? Combat Rifle or Assault Rifle will fit the bill. Long-range weapon? The Hunting Rifle is greatly suited to this purpose. The Laser Rifle and Plasma Rifle can also be modded to suit all three roles. Simply put, this is the only weapon skill you'll really need from the beginning of the game until the ending credits, at any level, against any foe, in any situation. No other weapon type compares to the sheer diversity and utility of the non-automatic rifle.
If you want to see a foe's resistances and level, well, you can drop a perk here to do it. It's never necessary to do so, however, and if you've got a properly built character, you'll never care.
There's a ton of loot locked behind various containers, not to mention all the doors. There is a work-around, however: you can always just take Cait along with you, and she'll pick any lock of [Expert] difficulty or lower, reducing the need for this perk. But if you want to travel with anybody else or - better yet - make use of the "Lone Wanderer", or in general don't want to be dependent on Cait, you'll want to invest in this perk. Or at least the first three ranks to be able to tackle any lock you come across. Bobbypins are cheap and ubiquitous, you don't need the fourth rank.
If you like to blow things up, this is the perk for you. Like many weapon perks, Demolition Expert increases the damage its covered weapons (in this case, explosives) deal with each rank, up to a maximum bonus of 100%. Being a somewhat limited set of weapons, however, it only has four ranks, which are fairly packed full of goodness.
At rank one you also get the ability to craft explosives at Chemistry Stations, at rank two you gain an aiming arc with thrown grenades, at rank three your explosives have a bigger blast radius, and at rank four you, well, also benefit from shooting mines and grenades in V.A.T.S., for what that's worth. It should also be noted that Missile Launchers and the Fat Man benefit from both Demolition Expert and Heavy Gunner, which makes them do stupid damage. The downside is obvious, however: explosives aren't terribly useful in every fight, and they're fairly uncommon and expensive compared to normal ammunition. Still, as a secondary weapon perk, it's not a terrible investment, just not a top priority.
The one exception to this is if you find one of the better legendary weapons in the game; an Explosive Minigun, Explosive Combat Shotgun or Explosive Assault Rifle. Since Demolition Expert boosts both the damage and area-of-effect on this already stupidly over-powered legendary prefix, it's worth investing in at that point.
Garbage perk is garbage. What you'll give for two ranks is a three point bonus to Intelligence and Perception, and only at night. The end benefit of this is basically a minute accuracy bonus in V.A.T.S. and a bit of bonus XP. Night vision while sneaking it kind of cool, though, but not two perks cool.
The Energy Weapon equivalent of Toughness - remember back in the good old days when Toughness just gave you resistance to all damage? Yeah, those were the days. Now you have to waste a whopping five perks to get damage resistance to half the common damage in the game. And how much damage reduction will you see with 50 damage resistance? Well, a bit, considering that a good, full suit of armor will get you around 100 damage resistance (to both energy and physical damage, mind you). On the other hand, one piece of clothing with Ballistic Weave Mk5 gives you 110 damage resistance against both types of damage. Armorer makes this perk absolutely worthless, and the fact that they're offering up five ranks of it is just insulting.
For a V.A.T.S.-based building that uses non-automatic weapons, you'd think this perk would be a no-brainer, right? Well, let's talk about this like reasonable adults. The first rank is rubbish - you should have enough AP to hold your breath long enough to pull off a headshot without this rank. The second rank is absolutely unintuitive to sniping, as if you manage to knock down your foe, follow-up shots aren't going to be terribly easy. The third rank, however, adds a nice bonus to V.A.T.S. accuracy, a brute +25%, in fact. This is the whole reason to invest in these perks, but is three perks for a 25% accuracy bonus worth it? Possibly, but for mid-range headshots with short-barrel rifles. For actual sniping, however, you should just make use of this magical thing called a scope. Then again, you can always get closer with a short-to-mid range weapon, or let Concentrated Fire boost your accuracy.
While this perk seem fine on paper, it under-performs in the actual game. First, while you can shoot foes behind cover in theory with this perk, you can't actually target them in V.A.T.S. if they're fully behind cover. A minor inconvenience - the real deal-breaker is the fact that this perk doesn't actually perform as stated. Often, while shooting at concealed foes in V.A.T.S. your shots will still be obstructed by the cover, which is kind of besides the point, no? It doesn't happen every time with any specific piece of cover, it's just a random nuisance you'll have to deal with that'll make you less likely to rely on this perk over time. It does work much of the time, however, so it's not a complete waste of a perk.
Depending on your build, Concentrated Fire can be an absolute devastating perk. If you're a V.A.T.S.-happy character with a fast weapon, you'll want to pick this up, even though it requires a whopping ten Perception to get, and the third rank requires you to reach the 50th level. Still, for this investment you'll end up getting +20% accuracy and damage per shot (after the first) that targets the same body part. So, say you have some V.A.T.S. Enhanced legendary armor with "Ultra-Light Build" mods on them, you can end up getting ten (or more) shots with one Action Point bar. Do the math. That's the calculus of victory there.