[Nem]

I've used earphones and IEMs for as long as I can remember (ety er6, se530, etc) and just recently decided that I need a pair of headphones for pc gaming and listening to music while I'm at my desk. I've been around a few different shops to try out headphones, but most stores only sell low-mid end gear (cant remember exact models, but I did try a pair of HD599s today). It seems that no matter what I try, (open back) headphones just seem to have a "weird" sound to them. They sound kinda muddy, and like everything is being run through a compressor. Its really hard to describe what I'm hearing but it certainly isn't the sonorous clarity that everyone describes cans like the HD59x series with
 
Is this a normal experience when transitioning from IEMs to headphones? Is it just a difference between closed/sealed vs open? I'm having a hard time enjoying music through headphones as everything sounds compressed and muddy compared to IEMs, but I'm hoping this is just something I need to get used to...?
 
I thought maybe it was an amping issue because I was only testing things through my phone (Nexus 5x), but I don't think any of the cans I tried are particularly hard to drive and even my IEMs sound great when using them with my phone...