Designing a class or sub-class with pre-specified class features and/or powers, aka "Essentials-style", is easier than one without because there are often fewer choices to make throughout your career.
For example a fighter gets to pick at least four exploits at 1st-level, one at 2nd, and so on and so forth all the way to 30th-level. The only point where new class features are gained is at levels 11, 16, 21, 24, and 30, which depends on the paragon path and epic destiny you choose. Conversely a class like the slayer chooses two at-will stances...and that is it. Your features are preset for you; +1 to attack with weapons, power strike as an encounter exploit, and you add your Dex mod to damage rolls. At levels where a fighter gets to choose utility exploits you get to as well, but a good chunk of level up will have you picking from a handful of class features or just taking what you get, like another usage of power strike.
This difference in complexity has lead some to believe that the designers at Wizards of the Coast are lazy, incompetent, pressed for time, lack the staff to properly design/playtest material, or a combination of all of the above. I think a major thing that the Essential-haters fail to realize is that there are plenty of gamers out there actually prefer these classes, or at least enjoy both, perhaps even at different times or for different game types. They seem to think that despite "everyone hating Essentials" or Essentials being a "failed product", WotC is simply trying to shovel out subpar content (that anyone could do) because they either have no other option, or just do not give a fuck.
Thankfully Trevor piped in to clear things up by page three, stating that no Essentials was not the result of lazy design or trying to get product out the door, but to provide an alternate entry point (as they have said), and because, yeah, there are gamers that want them, even if they are veterans. He even provides clarification on the vampire; it was designed to evoke the idea of a vampire in the D&D world, something that it does very well despite the limited options and thirty levels. Does a member of the WotC staff coming forward to clarify stuff and address concerns actually help? Eh...not really, which makes it no surprise that they so rarely do so in the first place.