Since a huge part of balance in this game is skill balance, I think it's reasonable to start discussing potential skill balances (both buffs and nerfs to certain skills). Since the vast majority of my time playing the game has been spent playing as a Magician/Monk/Priest/Invoker, I'll stick to what I know best and go with those classes.
Please note, the following balance suggestions are purely my opinion and subject to change based on skill balances we receive. Also, I'm not trying to state that my class is the only one that deserves buffs/nerfs to certain skills -- I wholeheartedly agree other classes could benefit from additional skill balances. I just wanted to tackle my main class, the class I know best.
Here are the skills that I feel need adjustments for the sake of balance (accompanied by my reasoning):
Fortress/Cannon Upgrade: I believe the main problem with these skills is that they become totally inferior to Diffusion Cannon/Double Shot at later levels. Even upgraded to level 9 or 10 (which I've tested), the damage for Fortress is only a bit higher than normal x-spam damage. Likewise, the bleed effect and additional damage on the Cannon Upgrade skill are underpowered. I'd advise buffing both the damage and the bleed effect for these skills, perhaps. Or, as an alternative, keep the damage the same, buff the bleed effect, and add an additional (useful) status effect, like a (decent) defense debuff, or something along those lines.
Slow Heal: This skill is overpowered, plain and simple. At level 10, you can restore 75% of your max HP over 30 seconds, 7.5% every 3 seconds -- that's overkill, if you ask me. Currently, there's almost no need for Monks'/Priests' Instant/Wide Heal/HP Restore skills, because Slow Heal does the job well enough on its own. Possible fixes include increasing the MP cost, lowering the heal amount, or increasing the time between heal ticks (lowering the overall number of ticks for the full duration).
Self Heal: This skill undergoes significant changes in the New Origins patch, so I'll reserve judgment until after I get to try out the new version.
Focus: AFAIK, this skill does not utilize Max MATK in its buff calculations, as many other buff skills do in New Origins. I think that's a little unfair, if it remains that way post-patch. But we'll see.
Meteor Rush: Currently, this skill removes Meteor Fall's ability to launch targets, which makes this skill a mostly pointless upgrade. I think it should still launch targets in the AoE.
Detection: Decent in PvE, but mostly pointless in PvP (except naked). IMO, decrease the debuff value from -100% MDEF to -5% or -10% MDEF, and make it use a target's maximum MDEF for the calculation rather than base MDEF.
Barbarian: This skill is fine when it hits, but that's the problem -- it doesn't take full Aim Rate into account to determine initial hit %, so it's mostly useless at higher levels, despite the fact that it's one of our very few catching skills. IMO, make the skill take full Aim Rate into account to determine initial hit % (keep the skill effect % the same, though).
Witch's Curse: Essentially the same problem as Barbarian. Doesn't take full Aim Rate into account, though it should, IMO. After all, even when you hit someone with this skill, it's canceled immediately when they are hit, and the cooldown has increased considerably in recent patches.
MP Recovery Increase: Unfortunately, this skill adds such a tiny amount to MP Recovery that it's worthless. It says it adds up to +30, but that's +30 MP Recovery %, not a flat +30 MP recovered per tick (which is what it should be, IMO, since MP Recovery already isn't terribly useful).
Wide Heal: Undergoes MP cost increase in New Origins, so holding off on commenting here.
Instant Heal: Same as Wide Heal.
Sanctuary: This skill is great at lower levels, but mostly useless at later levels. IMO, all healing skills should work off of a % of Max HP so they remain useful regardless of level. Mind you, the % of Max HP used to determine any heal amount should be reasonable, so that heals don't become overpowered.
Resurrection: Undergoes significant changes in New Origins, and it appears this will be much more effective. I'll reserve judgment, but at first glance I think the new version of this skill will be satisfactory.
Staff Mastery: Same issue as Focus, uses base MATK instead of max MATK, unlike other similar buff skills after New Origins.
Blessing: Same issue as Focus and Staff Mastery.
HP Restore: I'm sort of undecided on this skill. It's awesome that it stacks with Slow Heal, but unless you have massive MATK, the heal amount is much lower in PvP. In PvE, this skill rocks, though. I'd say keep it the way it is for now, but I may change my opinion after seeing New Origins and how things balance out with respect to other classes.
Barrier/Energy Absorption: These skills are decent at low levels or if you have insanely high defense, but for most players these skills are mostly useless as the amount of damage blocked is too low. IMO, this skill should act similar to Mana Shield, in that it blocks a certain % of Physical and/or Magical Damage, but I think the % of damage blocked should be much lower for us -- I'd say 5% PDD/MDD max would be reasonable, as long as the cooldown, MP cost and cast time remained reasonable.
Arch Sanctuary: Not terribly useful, the amount of MP recovered per tick should be increased, IMO. I'd say double the amount of MP recovered, but that's just me.
Quagmire/Muddy Mud: These skills undergo significant changes in New Origins, and I'm pretty satisfied with it on paper. I'll update this once I have a chance to observe them in action post-patch.
Healing Wave: The MP cost is too high, and the movement speed is too slow while using this skill. Also, it's too easy to interrupt. I'd say revamp the skill entirely so that it acts like this: You can toggle it, move normally while it's on, and while it's on it acts like an aura that has an AoE surrounding your character. At max level, once every 5 seconds it recovers 1% Max HP for everyone in the AoE (*excluding* the caster). It can't be interrupted, but it continually drains MP (a rate of about 1% drained every 10 seconds would be adequate, IMO). In other words,if you kept it on for a full minute, you'd be trading 6% of your Max MP to heal a maximum of 12% Max HP for everyone who remains in the AoE. Basically, I envision this as a sort of tactical support skill. Also, this revamped version would *NOT* work in BSQ.
Blood Fever: I used to think this was mostly worthless. But TBH, after testing it extensively in conjunction with MP Recovery Speed-boosting items, I found that this thing is a monster if you use it correctly. The only problem I have with it is that I think the MP Recovery Speed and MP Recovery % boosts this skills provides should be buffed a bit to make it a more sensible choice. After New Origins, MP costs are likely to become a problem for our class as many of our skills have had the cost basically doubled (not just heals, but offensive skills like Spark Rock, too) -- and that's not including the MP consumed using Awakening Charge to fuel Magnet/Wraith. For this reason, I think this passive could actually prove quite useful post-patch.
Lightning Magnet: This skill currently isn't too useful when dealing with targets with high Evade Rate/MSPD, but once we get the Aim Rate fix and Quagmire/Muddy Mud buff, it should become useful again. Updated opinion to be provided post-patch.
Wraith of Heaven: This skill is nice, but IMO the stun duration should be a bit longer. Also, it states that at max level it hits 4 times, but sometimes it hits less times than that, so it's either bugged or the description is wrong.