Allow me to apologize in advance. Being fairly new to all of this I don't have a good vocabulary for how certain headphones sound. I do own the Sony MA900's and certainly in comparison to those the mid bass on the 99 Classics is more apparent. The 99 Classics have more "thump" and present deeper tones. Is it exaggerated? Based on measurements I have seen, probably, yes. But I don't find it bothersome or unnatural sounding.
The tradeoff, in comparison to the MA900's, is the relatively tiny sound stage (I do have a good handle on that term, at least) and lack of space in and around the music.
I guess if I had to use a couple of words to describe the type of sound that the 99 Classics have they would be: visceral, close, punchy, and aggressive. About my only complaint is how the sound seems to be right between my ears (again, the tiny soundstage). Otherwise I enjoy them.