This is not an attack in any way, but what do you mean by "customization" here? Do you mean inside the rules or outside them, in the areas of fluff/backstoreis/gameplay?
To me the classes, with only one PP per build and only one ED in the whole first book, offer far less customization than classic 4E. Fluff/backstoreis/gameplay seem to be the same to me.
My group has decided not to do essentials at all. There are some nice options, and some AMAZING feats, but it is not what we want to do and does not fit with our playstyle, which is a gestalt-type way of making characters.
So we decided to not go that route and hope WOTC goes back to classic 4E stuff soon.
Well, you have to figure, by the time an average character has a theme, magic items, boons, grandmaster training, additions and subtractions due to background and character "fluff" (something I give bonuses and penalties for); play just gets convoluted. I like my players to have every options as opposed to none. Essentials just makes baseline characters, before all the add-ons, simpler to got in with.
Also, are your players even avoiding new feats? I don't think they have to separate themselves that much from "Essentials". Some of the feats are a lot of fun.
Just as a general side note, I think once the new character builder goes online, a lot of people are going to end up with Essentials feats without even knowing it. I know a lot of players with the old CB that don't look at the "source" at the bottom of the description.