In my own feedback, I'm using a set of premises - these might not be very useful to different difficulties and so. My experience is based around Veteran and Legendary difficulties, with as much as possible balance fixes applied from 1.2 list (as long as these can be done with ini edits). Lesser difficulties provide much less of an incentive to "min-max" class builds and allow you to pick whatever and still be strong.
Premises:
- Close combat is nearly always inferior to ranged combat. It's risky due to pod activation mechanic, and it may not be very reliable, leaving your soldier exposed. It is applicable when enemy numbers are low enough, but those cases are uncommon. As such, I generally expect melee perks and classes to show more potential than ranged ones.
- The game requires you to build 2 distinctive types of soldiers: ones that infiltrate, move, and stealth well; and ones that kill stuff well. There's no reason to mix and match approaches, since only one of these two approaches will be applicable to most missions outside of early game (this is well-explained in other threads discussing the lack of middle-ground missions).
- Heavy wounds are absolutely unacceptable. Whenever you play with Red Fog or not, getting severely wounded can easily lead to losing a timed mission outright, losing a soldier, or just losing a huge amount of time due to recovery. On the other hand, light (1-2 hp) wounds are not really a big deal.
- Trying to depend on RNG won't get you too far in the campaign. LW2 allows you much less "wriggle room" compared to LW1, and things such as squadwipes of your A team will likely mean game over with no chance of recovery. If a tactic works perfectly in 95% cases but leads to wounds/dead soldiers/squadwipes in 5%, it's not a very good tactic.
Shinobi
They serve a vital function, being the soldiers you need to take on infiltration missions, but at the same time this turns them into an extremely boring class that doesn't even fight in most cases, and even when the situation allows a Shinobi some combat, he can't perform well enough. While there are a few combat-oriented builds available, none of them work until MSGT, all are close-range, they're weaker than combat-oriented builds of better classes, and they prevent specializing in stealth.
There are a lot of defensive perks in the tree that can all be stacked on top of each other to nice effect, but in the end this effect is extremely pathetic. Most aliens simply attack the most vulnerable target (rather than trying to shoot your shinobi near them), but more importantly - no amount of dodge and defense will save you from certain attacks like Viper's constriction, and even a huge dodge score will only make a flanking crit a normal hit instead. Good luck surviving "only" normal hits from mutons, vipers, and other nasty critters.
There are quite some melee perks as well, but only straight stat-buffs (Cutthroat and Blademaster) are useful. Bladestorm is so terribly gimmicky that people make separate stand-alone mods to make it worthwhile, and even when buffed, it remains highly risky due to positioning - usually flankable and with lots of danger of pulling more pods, and interaction with certain enemies - using bladestorm against a muton, either voluntarily or not, can just harm your soldier. Coup de Grace is outright weak compared to damage-dealing abilities of other classes, and doesn't even work on a yellow move like Fleche. Sure, sometimes you can score a kill against a barely damaged sectopod, but sometimes you won't, and will spend soldier's entire turn doing nothing useful. And only Reaper makes melee Shinobi build somewhat useful, but Reaper chain usually goes around only until you hit a graze. Which might be your 1st attack as well.
Ranged damage build can function decently well, Hunter's Instincts + Rapid Fire is one of the most reliable ways to deal good amount of damage with a Shinobi. Serial works too, but pretty much requires you to pick a weapon other than SMG, thus forgoing mobility & stealth bonus. However, these builds aren't really compatible with stealth, as you're likely to pass on Ghostwalker, Shadowstep, and Covert. Making a ranged damage build "jack of 2 trades, master of none" - less effective and more risky on ranged attacks than, say, Ranger, and unfit to run full-stealth missions.
In the end, I stopped trying to use anything else than full stealth Shinobis. They aren't bringing anything to the table that can't be done more effectively with other classes. Stealth build is a must-have in the current metagame, but it's boring and skips most of the game's mechanics. Might as well make a "soldier" without any primary weapons at all, because it's not like they're needed.
Specialist
Very unique in what it can do, and thus being one of the most useful classes overall. Even if they won't even be near the fight most of the time. The perk tree, on the other hand, is utterly terrible and mostly it provides you with access to unique perks (useful) and a lot of filler (not useful in any situation). Overwatch tree is the worst offender here: first of all, OW isn't spectacularly useful in LW2 due to time constraints on many missions, second - it requires you to skip almost all unique perks, and third - Specialists get the weakest Aim progression, and it's unlikely that you'll get decent Aim even at MSGT.
As a whole, even while very useful, Specialist is just another extremely boring class - it doesn't do anything spectacular by himself. It doesn't need to be in the combat even, as GREMLIN abilities work on squadsight and Field Surgeon works simply by taking a soldier on a mission. Specialist can be a part of stealth missions, but primarily only for "greed" reasons, the only thing that your Specialist can do on a stealth mission that a decently-leveled Shinobi can't - is to hack the objective with much bigger hack score to get extra reward.
Initially I disregarded the idea of making Specialists into Officers, thinking that Specialists already have enough abilities on their plate to keep them occupied through both actions. Nope. They don't. Practically the best officers, with the caveat of being useless in direct combat, and thus requiring complicated positioning.
Assault
Another fairly unique but dysfunctional class. A shotgun specialist is quite unique (and better than a melee shinobi due to having effective range more than 1 tile and allowing 3+ weapon upgrades to be used), but usability of short-range skills is limited throughout the game. Arc Thrower tries to complement that, but is pretty limited due to cooldown and the fact that it's not dealing any damage. Even worse, shotgun-oriented build doesn't really function all that well until GSGT. On the other hand, MSGT Assaults aren't weak, their MSGT perk choices are all absolutely great and can be game-changing (well, except for Lethal, but it's still strong).
So what, am I expected to arm my Assault with a rifle until I hit GSGT? It's pretty bad balance that a shotgun-oriented soldier is quite weak with his shotgun until GSGT, but at MSGT it suddenly become quite strong due to extremely powerful GSGT and MSGT perks. Even worse, a stun gunner build is a joke until MSGT, and then suddenly MSGT stun gunner becomes one of the strongest crowd-control soldiers.
All in all, it's like PsiOps. Lots of babysitting is required, but the end result is quite useful (well, much more useful than max-level PsiOps right now). I'd very much like a smoother level progression.
Technical
Your dedicated haven advisors. Seriously, haven-related missions are the best for unleashing your powerful, but very limited "alpha strikes". Outside of that, it feels like an extremely overnerfed class "just because alpha damage can be game-breaking if you pool everything into it!". So, to make a Technical work, LW2 devs propose that we start with weak and terrible class that doesn't do anything good apart from 1 rocket per mission (that usually scatters away), and then we build it up until it's good.
Well... this approach actually works to an extent. A fully-leveled MSGT Technical equipped with a heavy armor provides pretty good explosive options for a mission, can be also good with grenades (especially if you luck out more grenade-boosting AWC perks), and generally brings something unique enough to be considered a part of a good crew. But for the most part you'll feel like you're leveling up your soldier just to make it less terrible (and not more cool, as with better classes).
On a good side, it's also one of the classes where perk tree holds the least amount of unusable fillers. As soon as Concussion Rocket will be improved to a level where it helps you more than it helps enemies - I think that Technicals will be decently good overall. But I'd still like to see more paced progression with rockets - weak starting rockets that could improve with R&D, which will in turn enable Technicals to be less bad at low levels without becoming overpowered.
(Grenadier, Gunner, Ranger, and Sharpshooters are all on the "better classes" side, and I'll write about them a bit later)