Note, I'm off work this week, so I'm trying to clean out some of my half-written blogs. I actually wrote most of this a while back, when Essentials was first released. I didn't post it because I wanted to see how long the Essentials uproar took to die down. It mostly has, though I do still see the occasional post complaining about it. So if it seems like I'm getting annoyed by stuff that happened six months ago, that's why.
If there's one group of people who like to complain, it's gamers. They are the epitome of the "Unpleasable Fanbase" trope. If you release a new edition, people will complain. If you make a feat overpowered, people will complain. If you fix that feat through errata, people will complain. If you make any changes at all... or fail to make changes, or release too many books, or don't produce enough books, or even breathe the wrong way... people will complain. If WOTC announced tomorrow that they were going to start mailing out $100 bills to all their customers, people would still complain.
So it's no surprise that Essentials has such a bad rap. With all the errata and splat books that have been released for 4e, Essentials represents the most drastic change. Except, it's not really a change at all, since it's entirely optional. The Essentials line basically contains simplified versions of existing classes. But - and this is the important part - it doesn't replace anything. There is absolutely no reason your Essentials Knight can't fight right alongside a normal 4e Great Weapon Fighter.
Now, it is true that when Essentials came out, a lot of errata was released with it. WOTC wanted to get as much errata out of the way as they could, so that the rules would be as final as possible when the Rules Compendium was released. This makes a lot of people blame Essentials for the updates, even though those updates would have happened anyway. Another sticking point with some people is that the Compendium - the most up-to-date printed version of the D&D rules - is technically an Essentials product, which makes some people think Essentials is non-optional.
Whiners had been wanting to declare the game 4.5 for a long time. Long before Essentials, I'd see message board posts that said, "There's so much errata out there, it's 4.5 by now!" So Essentials finally gave them something definitive, in their minds. Personally, I'll call it 4.5 if and when WOTC calls it 4.5, and even then it's just a number. I realize there's something of a stigma there (when 3.5 was released it caused an uproar), but to me it's just a way to let you know you're buying the newest version of the book.
The complainers would only need to flip through the Compendium a little to realize that the core game hasn't really changed. Other than the corrections and balance fixes that would have happened anyway, the game itself is still the same. All that's different is the addition of some new classes which play a bit different from the original 4e classes. Essentials, in my opinion, feels like you're using a 3.5 (or earlier) character in 4e. This is how WOTC tries to please everyone - by letting the 4e-hating grognards play classic characters alongside normal 4e characters (sometimes referred to as "AEDU" characters). Of course, when you try to please everyone, all you really do make both sides mad at you.
But they did manage to please me. I've only played a couple of Essentials characters so far, but I've looked over most of the classes and I like what I see. They're not always going to be my first choice; in fact, I'm probably going to alternate between Essentials and normal characters in campaigns that allow it.
Generally speaking, Essentials characters focus less on the 4e "powers" mechanic, and replace it with other bonuses at each level. But each class handles this differently. Fighters use basic attacks combined with stances. Rogues use basic attacks but have At-Will movement powers. Spellcasters are the most similar to normal 4e characters. This variety gives it the classic flavor. In the past, some have criticized that all 4e classes are alike, but Essentials classes break that cycle.
Despite the new classes being optional, some people complain that Essentials is turning 4e into 3.5. Am I the only person in the universe who likes both 3.5 and 4e? Is one edition better than the other? Is basketball "better" than football? Why can't people enjoy both, for different reasons? Every edition has highlights and flaws, and different people enjoy different things about the game. Personally I think 3.5 is better for roleplaying and simulationism, while 4e has a more interesting combat system. But I'd be more than willing to play either edition, regardless of whether it's a roleplay campaign or a hardcore combat game. (I won't go much earlier than 3e, though, for risk of running into my dreaded arch-nemesis THACO. Or that STR 18/99 thing. If your Strength is 18, it's 18. Period. I don't know what that /99 means, but if you write it on my character sheet, I'll stab you in the eye with your pencil. But I'm getting off the subject here.)
By all rights, everyone should be happy now. If you never liked 4e, then try playing an Essentials character. You might find it fixes some of the stuff you hated (unless your complaints are about something 4e-centric like Healing Surges, in which case you're a douche and your opinion doesn't matter anyway). If you liked 4e just fine the way it was, then keep playing with the old classes; they haven't changed. The bottom line is, you can like Essentials or simply don't use it. But. Please. Stop. WHINING!