I’ve started DMing a little bit of 4E D&D.
4E is commonly reviled by fans of other editions as not being “real D&D.” There are good reasons for that. 4E changed a lot of things about how the previous editions worked and 5th edition was largely a reversion of those changes.
One of the biggest changes was making every class function in essentially the same way.
In 3.5 and previous editions, every class had subsystems in the rules for how their specific abilities were used and how those abilities progressed as your character got stronger. Those subsystems varied from extremely simple (fighters and rogues) to extremely complex (wizards and clerics).
That variation in complexity came along with a variation in power. At higher levels fighters are still doing pretty much the same thing and aren’t nearly as useful as they used to be at low levels. Meanwhile wizards can now summon a protective warrior that’s about as strong as his fighter friend and still have plenty of magic left over for whatever they want to do.
The problem is usually referred to as “linear fighters and quadratic wizards.” Fighters and other classes like them have very few subsystems and thus get stronger on a linear path. Wizards and other classes like them get access to a wide variety of powers and abilities. This means they are prepared for any challenge and get stronger at defeating all kinds of challenges. Expanding in multiple ways, quadratic.
There were a lot of complaints about this from the D&D community for edition 3.5. Wizards of the Coast, the publishers of Dungeons and Dragons, listened and tried to make something that responded to those complaints.
4E gives all classes access to the same subsystems. Everyone gets about the same number of skill points. Everyone gets a class feature that is unique to their class. At first level everyone gets two at-will powers, one encounter power, and one daily power. Everyone progresses at exactly the same rate, getting access to encounter, daily, and utility powers at the exact same levels as everyone else. Each character class will have access to a different power pool than the classes.
This means that the characters can seem almost the same on the surface if you’re used to older systems. Previously each of the casting classes had a slightly different spell management system. In 4E they’re all the same.
Is this good? Is this bad? It’s really neither. It’s just different. 4E presented a new way to play roleplaying games that people were unfamiliar with.
There are plenty of other differences between the system, but the biggest and most noticeable one was making all classes “the same.”