Thoughts and Discussion: Kayle
Time to list some goods and bads about Kayle:
~ I like her ability power marksman aspect and supportive elements.
~ Kayle has a pretty bland kit, her E is the worst with this as it eventually just turns into an active where you have to press E every 10 seconds, before that it is a passive with a short downtime.
~ Her ultimate and passive are too strong for no effort. ~ ~ ~ Her passive is a huge source of her power, but it is very unnoticeable by the player and there-by also under appreciated, creating something more interactive for the player just be more fun and interesting to use (maybe something like Kayle heals allies when near them ("touch") (minion/champion), a much more noticeable heal if the target is in combat with champions (so very weak outside of this for new free sustain) (also same target cooldown) and in doing so grants Kayle her range and damage on a cooldown for the self passive which scales with cooldown reduction so she can unlock the permanent range mode with enough CDR (healing minions so she can get the range solo)). This would help tone down early game lane power and leave room for better feeling abilities on her active abilities. ~ ~ ~ Invincibility is simply too hard to balance for PvP games, this is one of the reasons why Kayle has been in either extreme of always picked/banned or barely picked. So it may be better to do something else and/or give her just a normal shield just so she can be balanced much easier in the future, invincibility ultimates is not a champion's identity. Attacking the invincibility here because it is just simply something that never will feel fair to go against, unless we go Taric ultimate status and create a long delay to it since it creates a decision to try to run away or burst them out because the ult lands, but then we would just have a crappy Taric ultimate.
~ Kayle's angel theme can be brought out so much better. An angel should be both someone that protects their team and is a mighty and powerful creature ready to strike you down where you stand! Kayle has glimpses of this as she stands now, but on a visual aspect is not seen at all just by looking at her abilities (ignore what they do).
~ I would like to see a large set of changes for Kayle, keeping in mind her angel theme and keeping her core identity of AP marksman-support.
Below is purely for fun! Again below is purely for fun! Need to say it again, that below is purely for fun! It will expand on brainstorming and creating something to work off of for more ideas,
Angelic Touch (Passive): Range: 300 units Whenever Kayle gets near an ally (minion or champion) she heals them for 5 - 40 (+20%AP) health, increased to 20 - 160 (+80%AP) health if the target is in combat with enemy champions or epic monsters, this can occur once every 6 seconds against the same target.
Whenever Kayle heals an ally (minion or champion) or collides with a champion from Righteous Fury, she gains 400 bonus range and deals 20 - 60 (+30%AP) bonus magic damage on-hit in an area for her basic attacks for the next 6 seconds, this can occur once every 9 seconds (reduced with cooldown reduction).
Reckoning (Q): Cooldown: 11/10/9/8/7 seconds; Cost: 75 mana; Range: 650 units Kayle blasts the target enemy with energy, dealing 60/90/120/150/180(+60%AP) magic damage, grounding, and slowing by 20/25/30/35/40% for 2.5 seconds.
Holy Fervor (W): Cooldown: 0.5 second; Cost: 30 mana + 1 charge; Range: 575 units Passive: Kayle stores Holy Energy every 24/23/22/21/20 seconds. up to a maximum of 5 at a time. Kayle's basic attacks on-hit reduces the current charge time of Holy Energy by 0.5/0.75/1/1.25/1.5 seconds.
Active: Kayle pierces the target direction with powerful light, dealing 30/45/60/75/90(+30%AP) magic damage to struck enemies and reduces their armor and magic resistance by 3/4/5/6/7%, stacking up to 15/20/25/30/35%, for 3 seconds.
Righteous Fury (E): Cooldown: 16/14.5/13/11.5/10 seconds; Cost: 100 mana; Range: 600 units Kayle dashes in the target direction, dealing 90/125/160/195/230(+85%AP) magic damage to struck enemies and stopping at the first enemy champion or terrain. Struck enemy champions are knocked back 500 units, minions and monsters are stunned for 3 seconds.
Intervention (R): Cooldown: 120/100/80 seconds; Cost: 100 mana; Range: 900 units Kayle covers the target allied champion or herself in holy light for 3 seconds, shielding them for 150/225/300(+120%AP) shield and causing the first enemy champion that damages the target to be suppressed for 1.75/2/2.25 seconds.

Kayle ult is a problem? Look around... invulnerability to damage and/or cc is hardly unique to kayle - both for self and for teammates.