You really feel the definition of your bass. Your going to be hearing the kick and various low end parts of your music separately vibrating into your back. You really start to notice from a mixing point of view how the low frequency energy is working. Another thing I like is when you have the Subpac2 vibrating in a chair. It sounds like a nice soft sub in the room. Creates a nice ambient low end warmth in the room combined with mids and highs of some speakers!
I have to say, coming from a great set of studio monitors, I still find this an incredibly useful piece of hardware! I can more reliably monitor the low end of my mix, and be sure that it will sound good on most any system. Because I make heavy bass music, I need this thing to work reliably with good tested results. And so far, it has! I wouldn't say it is as powerful as most people claim it to be (hence the four star review) but it is almost a necessity if you are a headphone producer or producer-on-the-go. While it may be pricey for some, others will see the great value that this product has.