NOTE: This was written before Friday's beta update. I've done my best to update it, but parts of it are going to be out of date.
I'm probably in the minority when I say that I enjoy the Evolution of Combat and think it's a good thing for the game, and for the last few months I've been spending more time on the beta servers than in the live game. Everyone who's played it has their opinion of what should and shouldn't change, covering every point from 'necessary' to 'just plain unreasonable'. Then there are a few things that absolutely do need to be changed before this monster of an update goes live, if only because it'll make things easier for us.
3: Everything is the same
One of the most common complaints about the update (after "this sux don't do it") is that the system they have in place for stats leaves little room for variation. If I have a level 80 weapon, the only difference between it and another of its tier is the ability to hit a different weakness, and sometimes not even that, as in the case of dominion tower gloves. It's balanced in the sense that no one weapon is better than another from its tier, but doesn't leave room for the kind of versatility that players are used to. Godswords are the strongest example of this: without their special abilities they are literally the same weapon.
Then there are the items that the new system doesn't seem to have a place for. When the prayer books finally received stats, they went from being unique items to low-level magic offhands. Now their stats are a bit more diverse, as low-level magic offhands that provide miniscule defense and critical hit bonuses. The same is true of defenders, which became incredibly weak offhand weapons that have a defense bonus, roles better served by actual offhand weapons and shields.
The solution is simple enough, and it's already on Jagex's to-do list. Unusual items should get different effects, as they have (slowly) been getting. They just need to get the balance right, and if the updates are any indication, they're getting closer.
2: Plug the Holes
The last issue comes from the fact that some tiers have more items than they do niches to fill. On the other end of the scale, there are tiers without enough. Magic is missing many pieces of equipment throughout the lower levels, and it's easy to reach the point where it just isn't practical to use older sets because of the stat gap between separate equipment tiers — gaps that are left over from the days when melee was the only style that was worth using.
It's especially noticeable when moving from low level melee to any higher tier. Rune and lower has a complete set of items, covering every combination and preference. The level 70 tier and above, on the other hand, is considerably more limited, with only a handful of different weapons; level 80 lacks a one handed crushing weapon and two handed slashing and stabbing items, to be specific, and there isn't a thrown weapon above 60. While it does leave room to grow, it could be years before items to fill these holes are eventually added.
But they will undoubtedly be added eventually. This problem can benefit any number of play-styles; new equipment can be added through monster drops, crafting skills, or quests. More rewards for different play-styles is rarely a bad thing, especially when the game supports so many of them.
1: Learning to fight again
This is the important one. They call the Evolution of Combat "Runescape's biggest ever update", and they probably aren't too far from the truth. But for all they've changed, there's very little information on how to play. There's not much left from the straightforward click-and-wait combat system of the past, but that's what the community grew up on. Whether it's a guide, a tutorial, a quest similar to Blood Pact, or even just a clearer equipment screen, they can't leave players to figure out combat for themselves again. That's how the beta currently functions, and a quick look around the official forums should be a clear sign that it just doesn't work.
Of course, that one also requires patience from players. It won't matter if they come out of it with the best combat of any MMO if players aren't willing to learn how to use it. A little bit of guidance goes a long way.