I will say right off the back that this is one of the most beautifully shot show i have watched this year.
The cinematography and set design is unparalleled. The CGI and special effects were great too.
The acting, music, background score, Ost.... Everything was amazing and showed that people have clearly put effort in all those areas.
In acting, I was blown away by Lee Joon. You bet, I wil be watching everything he stars in the future and will be rooting for him. The guy has serious acting chops.

However, the show heavily suffered throughout because of its pacing issue.
They mindlessly dragged a few storylines for it to go no where.
Regardless, I believe the core concept of the show was amazing and had potential to me explores more properly.

All in all... I loved and enjoyed Bulgasal Immortal Souls even if it did drag on in the mid section.