The only thing I can liken it to, in terms of the history of D&D, is Swords & Spells. A game which was not received well at all by the gaming public, and was quietly left to wither away. Today you can easily pick up copies of it on eBay for under $30 (you'll see it often listed for much more but don't be fooled). When you do get a copy in your hands you'll see it is usually in a pristine unplayed state. Maybe some minor shelf wear.
Because nobody played it.
What's wrong with Swords & Spells? Compare the simplicity of Chainmail, where a unit has just a few traits like movement speed and combat ability, this makes mass combat, or skirmish level combat fairly easy and quick to resolve. Now imagine you took Chainmail and added on the detail of an RPG character to each unit. Resolving even skirmish level combat could take hours and would be quite tedious.
That's a lot what 4th edition is like.
It's not an RPG, it's a skirmish combat game with layers of special abilities, maneuvers and all kinds of detailed tactical level combat options. If this had been marketed as a skirmish combat game with a box full of minis then it would have made more sense. A successor to the D&D crown it was not. However, it did find an audience as witnessed by the success of the Penny Arcade podcasts of live play.
Setting aside my personal feelings for it, I can see that it is a tight and well designed game. This video gave me some insights and made me think a bit differently about 4th edition. I'm still not a fan, but there are some good ideas in here.