An advantage of the essentials classes is that their ability scores were more focused. A Cavalier just had to worry about STR and CHA (and really, just STR), while a core paladin had to worry about STR, CHA, and WIS.
The weapon and implement expertise feats in Essentials are superior to the expertise feats from the PHB2, because they added some other element to the +1 per tier attack bonus.
you could set up a level 1 mage to do 8 automatic damage every round with magic missile. Start with a 20 in INT, and take the implement focus feat. EDIT: this is possible with the core wizard, too, if you use the errata for magic missile. I would allow players to use either essentials magic missile or the original “roll-to-hit” magic missile (which I would refer to as “Jim’s Magic Missile”).
My favorite spell comes from the essentials Red Box—“Slimy Transmutation”.