Really good bass always was pretty much impossible to achieve. People came up with all sorts of solutions. Do a search, with enormous horns and speakers built into walls there are people pretty much turned their whole house into a subwoofer. I heard a bunch of systems with really powerful impressive and deep bass. But never anywhere heard really good bass until I built my DBA.
The difference is hard to describe in a way people who have never heard it will understand. It is not so much that the bass goes really deep, although it does. It is not so much that the response is ruler flat, although if that is your thing it can be, and a whole lot easier than any other method. It is not even so much that the bass is clean and tuneful and articulate, although it is all of those and in spades.
Mostly what it is, the DBA gives a sense of envelopment, of being in the recording venue and space. This helps make not only your speakers but your entire room disappear. This is something that is heard, better yet felt or experienced, even when there is no apparent bass to speak of being played. When I put my subs on Townshend Pods for example the improvement was immediately evident in these terms long before any real bass was even being played.
I have heard plenty of mightily impressive bass. I have heard some exquisitely tuned systems that I am sure measure within a gnats hair of perfection. And yet I have never heard anything with that you are there sense of envelopment that is so easily achieved with a DBA.