I'll say one thing, having played the Delve at GenCon a couple of times (played a rogue and a wizard) I was pleasantly surprised at how playable and fund the essentials characters were.
The Rogue is encouraged to behave like a rogue, and be a mobile combatant, by movement powers that add rider effects to his basic attacks. That's a simple idea, but the effect was great fun in play.
The Wizard -- at least the delve version -- had some interesting changes that helped to speed things up. For one thing, attacks with multiple targets did not roll for damage, they did flat damage, and all the player rolls for is to see if he hits. This cuts down a lot of confusion and time spent rolling up those attacks. I liked it a lot.
All in all, we really enjoyed the essentials characters in the delve, and I'm looking forward to getting my mitts on the books.
-rg