So, I like to play the cleric/priest/healer in most games. When I got into ESO, I picked up a templar kitty and started to play. However, I noticed a glaring problem to my previous games and the way healing works: there is no targeting of allies. In most MMO's, I have to target a fellow player and then hit my heal ability. Now, with the one focused healing ability I have, it looks like it target's what's under my aiming crosshair. Or, does it? How does the healing target the player that it ends up healing?
Sounds like you may be falling prey to your habits of healing on other MMOs. Don't feel to bad I do the same thing still, as I'm sure most do. Healing in ESO has purposefully moved away from the click targeting of the traditional MMO. ESO healing is supposed to be up close and personal for the most part, obviously if you can target well enough with your target healing spells you can from afar. Which brings me to targeting, there is a soft targeting box around everyone (typically referred to as the hit-box in most games) that if you aim at you will target and heal that person. Now if you miss their "hit-box" you will heal either the lowest health member in your party that is in range or yourself.
No more shall healers feel bored battling static health bars, now we must look at floating health bars and chase them.
I have also found as I have started healing more that even when not aiming, yet within range of an ally with less health than you, your heal will heal them. I think this is a bit of a design flaw that is hopefully unintentional as it could make single target healing useless.
ESO turns you into a pocket healer - making it effectively less fun than, say, Wildstar. Literally. If you want your heals to land on the people who deserve them, you must follow those people around and don't cast heals until those people are hurt. "Hi, my name is Des, I am at your beck and call."
Don't kid yourself into thinking people in groups will understand that you don't always have a choice about who you heal... They don't care and you still get blamed for their failures.
I have been a healer in damn-near every MMO and I don't find ESO healing any more fun than it was in Tera or Wow BC or Rift or even SWTOR. It just requires more movement than some games. In fact, having no choice but to heal idiots infuriates me. I like being able to dictate who Doesn't get a heal, but have no problem not being able to dictate who does. That guy who just pulled a whole room of mobs to you? Yep... he gets healed. That guy who AFK'd in a hallway - yep. he gets healed too.
Soft-targeting for all the heal spells I've tested will heal the closest/lowest health person period (I'm sure there's some complicated algorithm, but I'm too lazy to look it up). You can stand right next to a target and have him in your reticle and it will still heal the jerk over there. All my testing was done with me and my target out of combat, though, so maybe it's AI is smarter when in combat (doubtful). Heals don't seem to default to you or people in your party if there are hurt people outside your party. I wish it did, so I could stop healing morons who deserve to die.
When it comes down to it, if you want any control over who gets healed, you have to outsmart their AI by positioning and timing.