If you want the short answer, it can generally be summed up by a distinct lack of agency over anything she does. If you want the long answer… well then buckle up because we’re going to go over just about every part of her kit and look at why it is a drag to use.
1. Her Healing
Mercy’s base healing is not bad. Not great, but its reliability makes up for its somewhat lower output when compared to Ana, Baptiste, or Moira. However that’s not where it falls apart. Mercy’s healing falls apart when her enemies start managing to land more damage than she can heal. Ana, Baptiste, and Moira can respond with Nade, Regen Burst, and Heal Orb. Mercy has no way to respond to that when it happens. Closest she’s got is Valkyrie which only gives +5 HPS and has an activation delay.
So, how does the Mercy player feel when someone inevitably gets gunned down through her primary healing? Well… helpless and powerless because there wasn’t really anything mechanically they could have done to prevent it.
2. Her Damage Boost
There’s a lot of things that can happen to make Damage Boosting useless and Mercy has control over none of them. If the boost target misses, Mercy is wasting her time. If the boost target doesn’t use their damage dealing abilities while they have boost, Mercy is probably wasting her time. Funnily enough, Boost used to be at least a little better from the perspective of Mercy actually having control over it. It used to apply if the boost was on when the projectile hit. So Mercy used to be able to pull things like hearing her Reinhardt throw Flame Strike and throw him boost for a few seconds to get more damage and ult charge. She can’t do that anymore. Now all she can do is give someone boost and pray they manage to accomplish something with it.
Does any of that sound particularly fun, interesting, or empowering for Mercy? No. No it doesn’t.
3. Her Resurrect
There are 4 things that can happen that can make using Resurrect impossible. First, Mercy’s ally dies in a spot that is just completely and utterly unsafe. Second, Mercy’s enemies are paying super close to her or where her ally went down. Third, Mercy’s allies don’t cover her when she goes for a Resurrect. Fourth, Resurrect has the longest cool down in the game at 30s. How many of those issues can Mercy directly influence? If you answered “None of them” then you would be correct. This is made all the worse by the fact that Resurrect is Mercy’s most powerful ability. Her most powerful ability that she gets almost no say in whether it is even possible to use. Cool.
Let me repeat that again for emphasis. Whether Mercy can use her most powerful ability or not is almost completely out of her hands. That’s a surefire way to have a hero feel like they have no agency and no ability to actually sway the course of a fight or match.
4. Her Chain Beams
Well, the most obvious problem with this one is if Mercy’s teammates split up, they are useless. The second obvious problem with this one is that a decent chunk of the skill of playing Mercy is giving the right person the right beam at the right time. Chain Beams being part of Mercy’s ultimate makes it so the reward for being good at Mercy is… no longer needing to be good at Mercy for 15 seconds. The third problem is that… in general auras (or projected auras in this case) always feel less powerful and more boring than they really are because the effects are heavily split up and its just difficult to see what the full effects of the aura was. In fact, Lucio had a whole mini rework for this exact reason. Lucio was crazy powerful but no one wanted to play him because his old 30m auras were powerful but boring, so they shrank and strengthened his auras and he’s been significantly better to play as ever since.
Well, we got ourselves a triple whammy here gentlemen. Any one of these 3 would be an issue. All 3 of these together leads me to claim that Chain Beams are in fact the worst designed mechanic in the game bar none. Yes they really are that bad when viewed from how engaging and interactive they are.
5. Her Blaster
Is actually fine. It is actually the most fun thing in her kit. It’s a shame that her most fun and interactive thing is the thing that she’s pretty much designed around never needing.
Don’t believe me? Why do you think Attack Helicopter Valkyrie is so popular? It’s because it is actually fun.
6. Her Mobility
Her mobility is actually still quite fun. However I do have beef with it.
Her rework added Valkyrie’s flight, the official Angel Hop mechanic, and the Superjump tech.
The first problem with that is… that’s a lot more mobility… which makes Mercy much safer. I am reasonably certain that the reason Mercy caught 14 or so nerfs post rework wasn’t always because of how much Value she could spit out but was instead because almost no one could stop that Value from coming out… which was largely caused by her gaining a crazy amount of mobility.
The second problem with it is that mobility is what I would call a Force Multiplier. Outside of baiting enemies into attacking you when they shouldn’t, personal mobility does not have a direct effect on either your allies or enemies. It can make it easier to apply Damage/Healing/CC where it needs to go and keep the hero alive longer to output more Damage/Healing/CC… but that’s it. So… what happens when a hero has hyper mobility but then has their Direct Output nerfed 14 times? Well… there’s almost no Damage/Healing/CC to make more effective… so the whole hero falls apart and becomes useless.
The third problem with it I touched on in problem 2. The only way to get direct value out of Mercy’s mobility is to bait enemies into wasting time, abilities, and maybe even ultimates trying to kill her and failing.
This is actually really satisfying, but is unreliable because her enemies need to fall for it, and good ones won’t. This also leads to Mercy feeling a lot more like a weird evasion tank with healing abilities than an actual healer.
The fourth problem with it… might be just me, but it is that Mercy is primarily all about skill with positioning, awareness, and timing. Her mobility changes traded out requiring positioning and awareness for a bit of mechanical skill. This might just be a me thing, but requiring Mercy to have mechanical skill seems much like forcing a round peg in a square hole. That’s not what she’s about nor should it be what she’s about.
So… all around… yes Mercy’s mobility is indeed fantastic, but it is incapable of rescuing her from the rest of her problems. Unless of course the player in question just really likes flying. Then it might.
7. Her Power Fantasy
It really shouldn’t be difficult to tell what sort of person would gravitate towards playing as Mercy.
The Cleric. Or… the MMORPG healer.
You know the one. That character class who gives up almost all damage output (or hides it behind a weapon/stance change so soloing with them isn’t miserable) for unmatched abilities aimed at keeping their allies on their feet.
Mercy still has all the mechanics she’d need to fulfill that power fantasy. She has her only direct means of dealing damage behind a weapon swap. She has mobility to theoretically make it so she never has to use her direct damage and to make it so it doesn’t matter who she’s trying to heal, she can get there and heal them. Other than that one direct damage option that’s locked away, every other ability she has targets her allies.
Where does this Power Fantasy fall apart? The Unmatched bit. If you actually want to keep your teammates alive as long as possible… you DO NOT pick Mercy. Ana, Moira, and Baptiste are all better at that. Problem is none of them fulfill the role of Cleric either because they all need to do damage… either to get their full value or to just not die.
Prior to her rework, Mercy did fulfill the power fantasy of the Cleric. Why? Because of Mass Resurrect. If you got it charged fast enough and used it well, you felt like you could theoretically keep your team going forever. You probably couldn’t, but that feeling that you maybe could was super important. Then when she lost so much of her team sustain… well… there was no place for the players who wanted the Cleric feel in Overwatch to go. That’s a pretty large part of why there was such a large stink about Mercy’s rework. People told them to play other heroes but there wasn’t another hero who did what Old Mercy did and New Mercy didn’t do it anymore either. So… they came to the forums to complained, and honestly at this point most of them have probably left the game.