The DT880 was my first real experience with a properly balanced soundstage. My first experience with a soundstage of any kind was the SRH440, and then I tried on the M50 and it was noticeably wider than the former. Both, however, have that sort of "tubular" soundstage to my ears, which is reasonably wide but not particularly deep. The M50's soundstage in particular seemed almost entirely a straight line, and I had trouble forming a center image, something that eventually drove me batty and resulted in a return.
The DT880 doesn't have any of these problems, though being open it probably shouldn't. I don't think its soundstage is huge, but it's definitely spacious, well rounded, and uses every bit of its space to spread out sonic elements, and I have no trouble getting a center image.