Better balancing of items, loot, statistics and more
Equipment is one of Diablo IV's most important things. Fortunately, a blog on this subject has already been published to offer some initial answers.
Overall, players want more variety in their equipment, with more choices to make, and not just a bunch of legendaries. The almost absolute domination of sets in Diablo III isn't something that many hope to find, either.
Between the frequency of legendary items, regular upgrades, stats, legendary affixes, runes and runic words, there are many different and varied demands, and it would be impossible to go through them all here.
This is something we'll go into separately when the time comes, preferably when the game has a public beta.
Problems with builds
The search for performance is certainly the main restriction applied to the variety of builds on Diablo III.
This is largely an equipment issue, as sets and legendary sets apply numerous damage bonuses, which multiply each other, making some techniques hundreds of times more effective than others. Offensive skills and spells that don't have such bonuses or synergies are completely ignored, at least at a high level.
In the end, the game has become a war of numbers above all, as can be seen in Greater Rifts. Builds almost never incorporate skills specifically designed to get out of certain situations, and in most cases the gameplay comes down to playing a steamroller full of defensive cooldowns that goes at the speed of an F1 car.
Many people hope for slightly slower gameplay, with more thoughtful and deliberate actions to respond adequately to the situation — all with a build of its design to reflect personal preferences and possibly equipment.
There is a huge debate and conflicting expectations around whether or not one can freely change one's talents and skills. This is something that depends very much on the overall balance of the game, especially the equipment.
For now, we can only hope that Blizzard will be able to accommodate different player profiles with different ways of playing.
