it's the lack of challenge, in my opinion. the combining and removal/revamping of most stats makes gear choices, which once were, you know, varied, perhaps even with a little give-and-take mixed in for some flavor, into the 'who's got the highest item level' game. WotLK dumbed it down, cataclysm lobotomized it.
Yes and no. Let me explain.
The stat changes weren't made for the learned player's benefit. We were always going to min max and calculate the specs and gear that gives us 0.1% extra dps. They're made for the newbie's benefit only; the guys that would chuck Spirit on their warrior because it gave them extra regen, or Strength on their priest so they could do more staff damage. For experienced players, stat changes are about the same - the addition of Mastery balances out the "useful" stat removal; ie the stats that we used in wrath, but are gone in Cata... not the ones we didn't use in wrath that are now gone.
You are most definitely right about wrath dumbing things down. However, it also includes the hardest encounters ever designed across all versions of WoW (excepting invincible cthun xD). It can be easy to miss sight of that when you see their new philosophy of difficulty levels that range from super casual what-is-a-mouse to holy-crap-where-is-my-health, to enable lesser skilled players and/or casuals to at least see some endgame content.
Where you're dead wrong, however, is Cata dumbing things down. From the looks of things, Vanilla is back... in spirit, anyway. Tanks are definitely more powerful than in Vanilla, but it's back to if you DPS the wrong target, you'll pull aggro. It's back to CC or bust. Healing has been transformed back from whack-a-mole-flash-spam to careful and calculated efficiency-versus-need healing. Even gear is back to Vanilla levels; heroic dungeons give blue items. Even BC threw in some epics at that level of content.
The one area that I'm not a fan of are dungeon points, and the "shifting window" of raid content. To explain: we saw it at the end of wrath. At the beginning of wrath, you'd level to 80, do some dungeons, do some heroics, craft some gear, grab some basic emblem gear, step into the lowest tier of raiding... even though the latest content was several tiers higher. At the end of wrath, doing simple and mindless heroics got you the second-highest base tier gear.
You were expected to skip Naxx, Ulduar, Sarth, Malygos and even ToC to a degree and step right into the "current" tier of raiding, ICC. I call that the shifting window of raiding. Had another tier of raiding come out after ICC, the "window" would have shifted up, where the bottom of the window grants T10 from heroics in order to facilitate you entering the top of the window, or T11 raids. This is bad because it means that a lot of endgame content is suddenly made irrelevant and obsolete; where making an alt in late Vanilla or BC gave you plenty to look forward to, Wrath just gave you ICC no matter what gear level your characters were.
Cata looks to be configured to use this same shifting window concept, which I am not looking forward to. Still, overall, Cata's a vast improvement on Vanilla. Push nostalgia aside for one moment and look at the good differences as well as the ones you miss.