Speaking from personal experience, my initial reaction to the Essentials Martial classes was very negative. I felt the loss of power options and reliance on MBA cut into my favorite thing about 4E.
To test them out, I built a couple, but I was utterly unimpressed with them.
Some time later, one of my players made an Executioner Assassin. While it has more options than a Slayer of Thief, that player strongly disliked the class. He would look longingly at the other players using Encounter and Daily powers before glumly throwing out another basic attack. On average, he cannot touch the damage laid out by the party paladin, much less the group's rogue. The entire party feels the character is more of a hindrance than an asset.
Over the summer I played a Hexblade. Though similar to traditional 4E classes, and fairly competent in a battle, I was very dissatisfied with playing the character, largely due to the limited choices of powers, feats and paragon paths (almost all warlock stuff is built around the curses). The character did his job, dishing out damage, but was not enjoyable to play, particularly at level up.
These experiences may not be typical, but they have dramatically shaped my perception of the Essentials line. I have not made any restrictions in my campaign, but I have not had a single player wish to use anything beyond the feats from the essentials.