These are some interface issues I have observed that I think should be addressed. I have tried to put these in order of importance as I see it. If you like these ideas please help me get noticed on the In-Game HUD DIscussion board on the official forums so we can get RIOT to address these. While comments here are helpful and insights will be incorporated, the fact is that RIOT does not look here for player feedback, so only by commenting on the offical forums can we get these issues addressed.
1. Facing controlled abilities: Several champions, such as Riven, Renekton, and Nidalee, have smartcast abilities that are targeted by their facing. These abilities can sometimes behave badly, usually because the champion unexpectedly turns just as they are cast to avoid a minion. These abilities should function by having the action occur towards the mouse pointer, thus moving control into the hands of the player and not the vagaries of the pathing algorithm. This is distinct from facing affected abilities such as Shaco's passive or Tryndamere's slow, which are fine because they are completely in the hands of the players.
2. Pets: The control of pets using the Alt key is awkward, as the key is not in a good position (requiring contorting the hand uncomfortably) and it is easy to accidentally miss and hit the windows key or the spacebar. While the ability to rebind it would be ideal, since all Alt-controllable pets but Le Blanc's passive are ultimates, it would make the most sense to have the R hotkey control the pet once it has been summoned. Your finger is already there and the key is not being used once the ult is cast, so it is the perfect method for pet operation. For Le Blanc, putting the control on T would work best, although having her passive be AI controlled would be even better, since the movement discontinuity that occurs at activation often makes it obvious which is the clone.
3. Floating Cone indicators: Several older champions including Cho'Gath, Annine, and Mordekaiser have indicators for their cone abilities that detach from them, even though they must move to the apex of the cone before casting. This causes numerous incidents where the spell is missed because the cone was imperceptibly detached, causing the champion to take a small step and delaying the cast. Please attach these indicators to the champion to prevent this issue (the behavior seen on Ashe and Shyvanna is ideal).
4. Range and target indicators: For difficult shots or for learning new champions, indicators are very useful. Several champions have ambiguous, misleading, or unhelpful indicators. A principle example is Fiddlestick's ultimate. The range indicator only covers his distance to jump, but gives no indication of the size of his ultimate itself. Other people with ambiguous indicators include Ezreal (his Arcane Shift should show the distance around his arrival point that is targeted) and Twisted Fate (his Wild Cards has a circular range indicator for a cone or triple line attack, making it hard to tell where the cards will go). Blitzcrank's indicator for his Rocket Grab is misleading, since it is centered on his body, but the attack comes from the right side.
5. Smartcasting, Selfcasting, and Keybindings: Due to the way keybindings are handled, it is often impractical to change the settings on a per-character basis. The default methods for smart and self casting are somewhat awkward, forcing many to adopt an all or nothing strategy. I propose that these behaviors be actuated with a double tapping mechanic, removing the need to rebind. If the ability is self castable and you double tap the hotkey when not on another character, it self casts. If on a viable target, it smart casts. This removes the need to hit a modifier key or to rebind every time you change champions. There would of course be an option to disable this behavior if desired. The modifiers can be left in place for use in rare ambiguous situations, such as large teamfight snarls.
6. Passive indicators: On characters such as Annie, Volibear, and Caitlin, the small icon indicating that the passive is available or showing the charging is difficult to see, especially later in the game when large numbers of aura icons are present in the same space. Since the passive icon in the main bar is not doing anything, it would be better to move the status indicator here instead. For On/Off passives such as Volibear, the glowing edge seen on passive bearing abilities like Vayne's Silver Bolts can be used to indicate that the passive is available, a timer while it is in use, and darkening when expended. For charging passives, a counter can be layered over the icon. For passives like Vladimir's, numbers could be put on the icon so the affect is visible at a glance. Alternatively, an indicator on the main health display above a champion's head would also be good for displaying the status of charging or On/Off passives.
7. Damage Types: Many ability damage types are not intuitive, such as Nidalee's Spear, which deals magic damage despite appearing to be a physical attack. While this was addressed on the receiver's side by coloring the damage indicators, it is easy to forget before the spell is cast for newer players. A small dot in the corner of the ability icon could indicate the damage or defense type to the user without being obtrusive. Attack damage or AD shields could have a red dot, magic a blue dot, healing a green dot, and CC causing or negating abilities a yellow dot. A divided dot could be used to multiple effect types. This change is mainly aimed at newer players.