Speaking from a caster perspective. Melees and Rangeds have their issues as well, but I generally find them easier to equip these days.
I have a lot of trouble fitting quality stats into my gear. Insightful to a lesser extent, but often the quality stats are very difficult to fit into my gear, as they don't appear in all expansions and when they do appear they are in items that you have a hard time fitting into your gear, either because of the set, the age of the item, or because of its characteristics or the slot of the item.
Insightful (+3) and quality spell mastery are also very difficult stats to find. They appear in very few items, and once again, they are items that usually collide with other important items. For example, ISM appears a lot in items with melee or ranged stats (not desirable for casters), in cloaks (it collides with sets when you want to run Magewright or Deacon of the Auricular Sacrarium), or in goggles (good goggles, but they also collide with Magewright). Clouded dreams is a very good ring, but it blocks an important set and has a penalty that weapon user items don't have.
Spell lores are also often difficult to fit, especially in a class that needs more than two spellpowers like the wizard (it's easier for a specialist with immunity bypass). Additionally, spell lore (the general one) is a nearly absent stat, and it also has too much difference with individual lores.
Insightful potency can be a tricky stat too, due to set collision.
Sacred spell DC is another difficult stat to fit. Frankly, I'm not a fan of this stat or the trend to gradually introduce more new stats (like profane doublestrike for melees). We have too many types of bonuses: competence, insightful, quality, profane, sacred, exceptional… I'm sorry, but gear has become a complete pain with so many types of bonuses on so many different stats. And it doesn't help that there are very few consolidated items, and often the stats appear in a somewhat random way.
I would like to see the spell points bonus set from legendary greensteel appear in the future as well. For some reason, it is completely absent from modern sets. Some sorc players might not want it. Here a wizard/cleric player would warmly welcome it.
Sharn was so successful because it had sets with consolidated stats and thought specifically for each playstyle in the game, along with other more different items that allowed to customize the builds. We need more items with specific design for playstyles and with consolidated stats, as happened with Sharn and to a lesser extent with Feywild.
IoD was so successful because it allowed customization through crafting. This allows to reach a greater number of builds than finished items and completely lacking customization. I miss more customization in the items, more crafting possibilities. Very often when you are making a set it is completely impossible to introduce an important stat, which does not fit in any way. Crafting allows you to bypass these problems.
I ask you not to abandon Randall Lyric. Augments are very useful for balancing the gear.
I ask you to do something about the +2 DC augments for each school from Gianthold. For builds like wizard they eat up almost all the augment slots. You give very little help to builds that need to equip more schools and more spellpowers, and it is one of the reasons why these builds are far behind specialist builds like sorc, druid or alchemist. Creating new higher level augments that give the same bonus to several schools (I'm not asking for them to go above +2) could help a lot to wizards, who really need to equip too many stats compared to specialists.
And finally, I ask that in addition to more consolidated stat items and more crafting, you stop breaking stats in several, like Resistance, Sheltering, etc. An item with +13 fortitude, for example, is a waste, because you know it's practically impossible to fit items that also have Reflex or Will into your gear. Shaltering is easier, but you keep adding more and more types of bonuses, and there's just not enough room in our gear for everything.
I also think the moon/sun system is going to need some tweaking. It suffers from the stat splitting effect, like resistance and sheltering did. Needing more items for the same stats or even fewer stats promises to be frustrating in the future. Added to this is having fewer set ítems (no rings, no weapons…), which will only make the problem worse.
I'm asking you to stop the madness and help us equip ourselves more easily. It's gotten to the point where a lot of people are desperate for loot. Yes, some people like this madness and play tetris, but most of us are already very tired. We've gone from ignoring all new loot until an expansion comes out, to looking at expansions and deciding they don't help either.