Ok, I don't want to reinstate the classic flamebait, but I'll give you a few examples on how the old way induced cries of "sameyness".
Assuming your non-human, you have 2 at wills, 2 encounters (one racial), and 1 daily power. Not counting basic attacks (or P42-inspired "stunts") you had four options in a given fight. Before I go any farther, I realized D&D always limited your options (fighters attack, mages have 1-3 spells, depending on edition, etc). However, the 4e power system creates an illusion of choice of sorts; OMG I have 4 cool options to use; which do I do? The problem is the options aren't all that different; the amount of weapon die (or spell die), the effect offered, and perhaps the defense targeted changed, but the difference between attacks wasn't as diverse as wizard spells nor as simple to adjudicate as fighters roll-n-forget.
This was further compounded by the fact early in, "the Math" wasn't all that great. Some monsters (particularly soldiers) were very hard to hit. This meant most of the time your encounter power (which you relied on for big damage or battle-changing status effects) was wasted. And dailies were too precious to use willy-nilly, so most people spammed At-Wills because they were "reliable".
Further add on that many powers were simply "X damage + Y effect" and you had a lot of powers that looked samey on paper (even if they weren't in play). Who cares if you use your shield to push your foe back or blast him with a bolt of arcane magic from your wand; your still just doing 1d8+3 damage and push 1...
Furthermore, classes within the same role ended up (for balance) having the same role-based mechanic. Every Leader got a X-Word power; it didn't matter if you were invoking the power of the Gawdz, yelling quotes of inspiration, or singing them a merry tune, the effect was similar. PHB1 had the same problem with strikers, warlocks and rangers call whose "it" and do extra d6s of damage. Rogues do an extra die of damage, but pay for it by setting up CA. Defenders mark; etc. While this was done to keep character's "viable" in there role, it also made them interchangable mechanically with one another.
Lastly, there were plenty of cool "deviations" in flavor that didn't do much mechanically. Druids could shapechange, but it was so useless all it did was restrict what powers you could use in a given round (by restricting powers to human/beast form). Shaman's got a spirit pet, but it was nothing more than fancy spell-effect and did the same X dmg/Y effect thing; no OAs, no CA, etc.
Oh, there's the "don't break your archetype" rule. It took Fighters till MP to fight two-weapon, and they still stuck at bows/missile weapons. On the other hand, a ranger can't be a decent sword-n-board fighter; grab two blades or a bow bow. And heaven forbid a rogue wants to fight with two short sword and a short bow. What were you thinking, get yourself a dagger and a crossbow like a REAL rogue!
And that doesn't begin to touch on how some early monsters were sinfully boring, magic items lacked anything "magical" about them, early modules was one show-piece fight after another with little rhyme or reason, etc.
My feeling is almost 2 years later, they've learned from there mistakes. Even if its artificial, I get a feel from the warpriest, mage, and knight they are separate classes with different roles and different abilities. They don't use the same "pick 2/1/1" formula, they are unique against each other. Magic Missile is guaranteed damage. Cleric powers depend on their god. Fighters augment basic attacks. I can't WAIT to see what the rogue does!
In short, for the first time these classes feel like separate CLASSES, not different fantasy tropes stapled to the same frame and called unique. I'll wait till Sept to see if I'm right...