Yeah, that sounds like my experience with the open M1570. It's very technically capable and plenty musical, and yet there was just something about it where, in the moment when it was on my head playing music, well, it was just boring. I don't know if it's the dynamics or transient speeds or what, but, just... it's the only headphone I've heard that made me forget I was listening to music. It was only slightly more stimulating than sitting in silence and thinking about music instead of listening to it.
for me the M1570 actually could image wider than the DT1990... I once had an LCD-2f with what I call a "cardboard cutout" soundstage, the angular direction of images was somewhat vague, it seemed like they dissipated so your ability to find the angle of an image was cut to about 5-10 degrees of surety.... But the distance-based imagining was insanely pinpoint, and even images close together you could "hear the silence" between them in the distance, it was jarring and uncanny.... So I equated it to images being cardboard cutouts with notable width but no thickness to them as if I was surrounded by cardboard cutouts.
The M1570 IMO has like no separation, everything is blurred together in every which way and envelopes you..... Sound is everywhere and all encompassing, you can't "hear" the silence.... I honestly prefer the M1570 over the DT1990 or anything under $500 too, but there is no playfulness and you lose plenty of titillating details in the mix sadly.... It's great for lots of bass music, electronic, feeling like you are at the club or intense low end heavy songs and male vocals.... but it suffers on the upper range for it, engulfing bass or low male voices are one thing, treble and sharper female voices aren't as pleasant for that nearly across the board...
I also put the M1570 against multiple LCD-2F's, LCD-X, and LCD-3
The M1570 won hands down until I jumped from $500 source (Monoprice THX 788) to $1,000+ (Oppo HA-1)
Here is how it went
Under $500 sources M1570 beat the LCD-2F, was edged by the X and 3
$500 source the X and 3 got a good bit of headroom but already they were maxing source and showing it's weakness, M1570 Edged LCD-2F's
OPPO HA-1 Both M1570 and LCD-2F unbalanced were about even, down to preference
Didn't have balanced for M1570 but Balanced LCD-2F started to edge it, at this point I would take the 2f, the X and 3 left both in the dust
Above this the LCD-2F maxed out with little benefit balanced, but the M1570 unbalanced had already maxed on the HA-1. the X and 3 added more and a noticably more, respectively
The M1570 is a good choice for people under $1000 who don't want to invest in balanced aka budget, and if you have $500 gear no joke it beats the LCD-2F as it's not as source dependent but even at $500-$1000+ I think it's preference, if you highly value separation and "empty"(not bad just open sounding) the LCD-2F just wins, if your idea of a good time is the HD600 soundstage but with actually depth, a tad of separation, and decent angular directional imaging I think there is no reason to pay more for the LCD-2F even if you have $1000+ source gear.