There are a number of Essentials classes. Maybe some are inneffective and others overpowered? That's one of the interesting things about making a system a little less balanced - play style differences will cause it to break in different directions for different groups. One group is awed by the Knight, another finds it worthless unless powergamed to the hilt.
And the balance is still pretty tight - a lot is in who is playing the character. And a lot in the build.
My experience playing a Mage in Encounters was that BS was /very/ tempting on almost every round, especially with an Enchanter (push 3? no, push /6/). Especially the season when there was also a hunter, and pushing enemies into a tight group set him up. I guess you could say that BS was so broken, it made the Hunter effective.

That's propper old-school teamwork - casters setting up martial types and helping them suck less.
And my experience playing a human orbizard was that I had Beguiling Strands as my third At Will - and never found a single good use for it. My main line damage and mookbashing at will was a (sometimes expanded) Freezing Burst. Slide 2 is IME at least as useful as Push 4. (It didn't help that our tank had resist cold so I'd happily ground zero the enlarged freezing burst). And because FB has a damage
roll it can actually do decent amounts of damage. My second At Will was Storm Pillar - incredibly effective in an urban environment. And rocks for an Orbizard with his at will extension ability.
Beguiling Strands is a powerful at will at low levels - but cast by a 13th level mage it will do a stunning total of 6 damage at best. That just doesn't cut it except in very rare circumstances or with seriously big terrain features. Freezing Burst on the other hand has damage that keeps up. Because it's a damage roll it benefits from your implement bonus, your implement focus, dual implement spellcaster, and other things.
As for the hunter not being effective? They certainly aren't bad (even if I do build them as humans with Twin Strike most of the time). They almost invariably IME win initiative and Turn 1 involves them providing an overlap by using disruptive shot (at +2 to hit from the stance) to immobilise a brute (save ends). That's one enemy monster out of the fight for an average of two rounds - you've just given the PCs the overlap. And judicious use of Clever Shot can make it a second. The hunter therefore does his job by making the enemy not reach combat. And providing some pretty decent damage. Oh, and sneaking like a rogue and having decent perception. Or at Paragon mangling solos (seriously, blind? Three to four times an encounter?)
A Slayer, yeah. A Theif doing the Tactical Trick shuffle, not so much. Again, IMX, players have fun with a Slayer, for a little while, but the Theif is rarely a hit - if you don't figure it out, it's ineffective; if you do, it's boring.
Thieves excel outside combat. Seriously, seven trained skills
and a climb speed? And the Tactical Trick Shuffle is competent rather than skilled play. Tactical Trick is what you use when you have nothing better to do if you're tactically inclined. It's solid play - but there's an obvious next level of play above that; using your tricks that grant bonusses once you have combat advantage like Acrobat's Trick (with its climb speed), Thug's Trick, Tumbling Trick, or Unbalancing Trick.
Oh, just little inconsequential things, like class balance. Nothing that should be important to a /real/ D&Der.
E-class balance is IME pretty good. Not found real problems either way except in single encounter days.