My experience with the LCD-5 is almost exactly the same - when I first got them I was quite disappointed to be honest, they sounded clear, transparent and detailed but seemed very "flat" to me, with very little macro dynamics and lacked punch. They are very intimate, the soundstage was pretty narrow and I was regretting trading in my LCD-4s. I was taking a chance on the trade-in as I mostly use my Susvaras these days and was hoping the LCD-5 would provide an easier to power all around headphone, maybe somewhere between my Susvara, Utopia, HEKse and LCD-4. I listened to them exclusively for about a week and although they improved (I'd say brain burn in was the cause) I still felt they were, for lack of a better term, "boring".
But now I'm on week 2 and somehow they have almost transformed - I can't really explain how or why, I'm not really a big "burn in" believer but they now have much more punch and sonic weight to them, the tuning was always good and separation of instruments always stellar but they've added a new dimension of tight, controlled precision and richness. Timbral accuracy of instruments like bass drums, guitars and acoustic bass have the proper frequency response and unparallelled realism, punch and weight that I originally found lacking. They still sound a bit closed in compared to Susvara, LCD-R and HEKse but there's an addictive immediacy and precision that even bests Utopia.
I don't find the treble rolled off at all, in fact there are moments when the high end gets a touch brittle depending on the recording - I have no issues with the clamp force, headband/yoke size or the look of the acetate rings but I do much prefer the old LCD template given I had no problen with the weight. In fact I find the LCD-R more beautifully built and also more comfortable overall than LCD-5.
For reference, I am using a Bryston BDA-3 DAC with a Luxman P-750u headphone amp, and although the LCD-5 has been billed as quite easy to drive, I find it still needs lots of power to sound its best. I did not and don't use any eq at all, but I can see why someone might want to with these.
All these superlatives aside, I still think Susvara reigns king for me, but LCD-5 is another major achievement for Audeze.