Tony Vargas
Legend
If you're making changes that make your game no fun, you really kinda suck as a DM, and you probably shouldn't be 'empowered' or 'burdened' any further.The difference is the ability to do this is directly related to what the players will let you do. In a home game you can make your players angry and lose players if you make changes that make the game no fun for them.

We haven't seen any of 'em yet, so we can't say. What I heard in the article at least suggested that part of the point was to be able to make up items without worrying so much about balance - that 'rarity' becomes the balancing factor. Again, this is something that was done quite a bit in prior eds - and never worked that well.Rare items are balanced when used in the recommended fashion(1 per PC per tier with a 50/50 split between their common items and uncommon items).
I have only heard the claim that they are 'compatible.' They litterally /can't/ be balanced to the extent existing classes are. They almost certainly /will/ balance at some intersection of encounter difficulty, number of encounters per day, and information availability. It's up to the DM to find that balancing point and stick to it.Essentials classes are designed to be balanced with all of the previous classes.
DMs should not have to adjust any encounters at all simply because everyone is playing Essentials classes.
That's not DM-empowering, that's just player-limiting. And, players don't like being limitted - and they know the DM can give them that 'special permission,' so they'll try to get it. If items are balanced, and players can make/buy what they want, the player is 'empowered' to customize his character a bit, and the DM doesn't have to worry. But, items have to be balanced. If items /aren't/ balanced, but the players can't easily obtain them, then you can bet they'll try really hard to obtain them. "What 'reagent' do I need to make a Phylactery of Brokeness? How about a +6 Gamebreaker weapon? Have I heard legends of such an item? blah, blah, blah..." Of course, you can use all that as adventure seeds - if you really need adventure seeds - but, if you do, the PCs going to be expecting the item at the end.The reason magic item rarity is designed to give DM empowerment is because the system says "Players can't buy Uncommon or Rare magic items nor can they craft them without the express permission of the DM". It enables DMs to do LESS work to police their game.
Again, this is not some brilliant new idea. Rare and uncommon items work /exactly/ the way most magic items worked in AD&D (both eds). In those day, magic items /routinely/ defined characters who obtained them, overshadowed PC abilities, and wrecked campaigns. A good DM could keep that genie in the bottle, but it wasn't exactly a walk in the park. Unlike with the Essentials martial classes (which, at least, face less overwhelmingly potent dailies in the hands of their fellows this time around), I see no reason to expect it to go any better than it did back then.
Worst case: we start seeing 'common,' 'uncommon,' and 'rare,' magic items in booster packs....
The new rarity system assumes one rare item per tier, and about half your items being uncommon - players can't make or buy them, but 15th level characters also get to /pick/ a 14th, 15th & 16th level item. If you allowed only common items, they're going to be decidedly sub-par. So either you're going to have to let them pick their uncommons and rares, or you're going to have to do it for them, or you're going to have to dial down your game a bit.They can simply say "Make up characters using the default rules. Everyone starts at 15th level." and not worry that someone will come into their game with something like Frostcheese combinations.
Then, there's all those characters already in play. They have a lot of uncommon items. They're not balanced out according to the new rules. You're going to have to take items away from them or something.
I can't read the developers' minds and say with certainty what they're designing classes to do or be. All I can do is look at what we've seen in previews. What we've seen is a lot of stuff that feels very much like it did in prior versions of the game.The Essentials classes are designed to have less complicated status effects and game mechanics so they can be more easily understood by players and new DMs alike.