the goal isn't "to level up". The goal is either to progress, or in case of sandboxes, it's left to be defined by player
Yeah, in fact I almost wrote "to progress", but changed it because that could easily be confused with storyfaggotry and we're talking about game mechanics. New story/world content is a reward structure in basically all games but I wouldn't consider it a part of the game mechanics.
It's a part of what motivates player. Player doesn't want to be bored, experiencing new stuff helps with that.
In mechanics terms, progression in a game like PoE means gaining access to new abilities and items, IE leveling and finding loot.
And since new loot doesn't magically sprout out of your body just because you killed a lot of shit, new levels don't necessarily need to as well.
Goal XP is basically devs' way of saying "I have a good enough idea and control of what individual player's experience will look like that I can decide what the major accomplishments will be".
It's basically yet another layer of:
Small <-------------> Big
Hand-made <-------------> Procedural
Static <-------------> Dynamic
...
Goal XP <--------------> Use-Based
Where stuff in the left column synergizes with stuff in the left column, and stuff in the right column synergizes with stuff in the right column.
This doesn't conflict with Burgun's point, except insofar as Burgun recommends one of the systems being primary.
Well, stating that in an RPG/any sandbox *NONE* of the systems should be primary kind of conflicts with statement that one of the systems should always be primary.
That's why I suggested he sticks to mobile/FB gaming - he obviously can't wrap his head around anything bigger and more complex than that.
I'd even argue that short-circuited and tightly coupled action-reward mechanics makes for bad games.
Short action->reward cycle just can't accommodate much gameplay complexity and diversity, while tight coupling makes performing particular action a nondecision - and I'd argue that all but simplest games are basically decision making simulators if dig deep enough, with varying amounts of what's basically interface mastery thrown in (can be 0).
Kill->get XP is such a short circuit that renders the decision of whether to kill moot in large amount of cases.
Similarly, take DX:HR and it's "praised" (by some) XP system - whether or not to take down a hostile is a non-decision (of course, preferably nonlethally, preferably by double takedown), whether to hack something is a non-decision (obviously) and so on.
Such short cycles basically amount to masturbation.
I'd argue that the 'core mechanism' in DOOM is damage avoidance, with killing enemies being a major supporting mechanism. The purpose of those mechanics is to be able to explore the level (you're scored by % items/secrets/enemies), with the overall goal being to 'solve' the map by reaching the Exit. Given that, new guns being placed around the map is a logical reward structure and fits pretty neatly into Burgun's model - it's a direct reward for completing the 'core purpose' and it supports the core and secondary mechanics.
Pretty much the same summary can work for an RPG.
Damage avoidance or mitigation is paramount because otherwise you die which prevents you from completing your goals, while reward structure can be tied to game's spatial and (in this case) narrative structure (quests).
No-combat XP system is a perfect fit for subsets of the genre where you can go through 90% of the game's content without engaging in combat, no argument there.
Not so sure about the game where (as AN4CHID already said) every class is valued by its combat effectiveness ( outside it, the difference seem to be minimal/negligent, a rogue is slightly better at doing roguey stuff than paladin) and in which I wager you'll tackle most of the game's content with combat.
Why if it's combat agnostic?
Because people have different expectations from different genres, they're wired to expect loot and XP rewards when they prevail in combat in a combat heavy RPG (like PoE by all accounts will be). Besides, even Doom and Thief gave you other incentives to explore their levels (gold to satisfy level quota in Thief and weapons/ammo in Doom), it doesn't have to be either/or, I can enjoy a battle with a Dragon from a tactical/combat gameplay standpoint but being rewarded with suitable loot/XP after such a battle would also serve to increase my enjoyment of it.
Fuck this shit.
Is PS:T a bad RPG because it defies so many cRPG expectations?
No.
Thrashing expectations is about the only way to create something new.
And that's my main issue with it, though it obviously depends to what degree is objective XP=quest XP in the final game. If kill XP encourages you to kill everyone in sight, quest only XP encourages you to do every little shitty sidequest you run into even if when it makes no sense whatsoever for your character to engage in it.
And that's why Obsidian should go all the way with it and ask what quests/goals should yield XP to begin with.
They probably won't but their system is still far superior to kill XP while remaining robust and lightweight.
Why couldn't they just remove XP gain from the enemies someone just stealthed past if it's so bloody important?
Exactly - why not build and balance a system only to arbitrarily overrule it at every step with elaborate scripting?
I don't want them to actually do that, but it would be much better than what they're doing now. I just want combat XP, stealth XP, quest XP, dialog XP etc.
And I want a donut.
Of course you're making a choice, but not between combat and pacifism, because there are no specifically pacifist/diplomatic attributes.
Why should it even matter? We're talking pacifism on individual quest or even encounter basis, not dedicated rat diplomacy builds.
is not a learning animal, then. 
