I was a huge fan of enhancement in Vanilla, continued to play through BC (though not viable), and played quite heavily in WotLK.
The changes in cataclysm (hate you Ghostcrawler... can't tell you that enough) really ruined enhancement for me, and it has remained relatively unchanged since then.
(1) I feel like the specs lost their theme. Blizzard continues to claim that each spec has its own relative "comfort element" elemental-fire, enhancement-wind, resto-water, but anyone who plays knows this isn't true. You have a huge mix of elemental abilities sometimes even more than your "core" theme. The argument could be made that the shaman is a master of all elements and thus should use them all... and I could see that, I prefer it the other way but to each his own. However, I feel that some enhancement abilities would fit better thematically with elemental... and vice versa.
(2) Lightning bolt, flame shock, searing totem, lightning shield... its all the same shit, with a different spin. I would like to see more unique spells specific to a given spec. This could tie into making the specs more unique thematically.
(3) Hybrid, yet heals suck ass... there are PURE dps classes/specs that do a better job at surviving/self-healing than shaman do with a spec and spell specifically designed for the purpose of healing.
(4) clutter, 3 shocks, tons of totems, spells upon spells, its Xzibit designed the shaman class (Pimp My Ride... look it up). Now I know that on the whole ability pruning is not a popular design choice among players. But I personally don't like to play with more than 20 (active) ability slots. Many other classes have several abilities wrapped in a nice neat package. To achieve the same goal a shaman may need to press several different buttons to get the same result.
Example:
Shaman: flameshock (applies dot), lava lash(spreads dot), fire nova(aoe damage), frosthock(for the slow effect)
Deathknight: Howling blast does all of this
Personally I think DKs play more like enhancement of WotLK... many of you are undoubtedly going to respond with, then play a DK. But again going back to theme I prefer my shaman.
I know that people's concerns are utility and performance, and I would agree the last thing the game needs is more homogenization. Personally though I look at my shaman and I think what a mess... little or no direction design wise, just a mess... make the mess work... don't worry about cleaning it up.
Lastly, and I think this speaks volumes to where the class is. Talent choices and core abilities/rotation.
Talent choices really change the core rotation of the class/spec. On top of that talent choices have a greater effect on performance when compared to other classes. Meaning there is a definite best choice, and a definite wrong choice.