I rolled a random "R" this evening and immediately reached for "Riverside". They are without doubt, Poland's best progressive metal band.
I'm not at all sure why I ever became aware of this band in the first place but they are good - really good! Take an ounce of Opeth, a teaspoon of Tool and stir in some Styx. (well maybe not the last one?)
There's some great riffage and tasteful instrumentation throughout and Mariusz Duda's big Polish accent shines through it all.
Unfortunately guitarist, and co-founding member, Piotr Grudzinski died suddenly just a couple of years ago. They continued on after a spiritual hiatus.