Thank you guys for all replies, I'm gonna definitely consider that. Now i'll take some time to think about it and probably buy something next week. Right now I'm a bit towards Blood Moon (but it's constantly changing) as it adds some more cards and horror theme is at least "ok", but from the other side I dislike the werewolf character and his mechanic. Firelands and all that tokens, ifrits and terrain cards sounds pretty nice for me, but I'm a bit afraid that it can ruin the game, when it comes to play just on main board and everyone won't find a place to regenerate and simply rush CoC at all cost or die trying (but yeah it's sounds like a challenge ).
That can be a really good thing as burn effect increases chance of draw a new cards, but it not happens so often like in just core deck + Firelands.
It's nice idea too, but Nether Realm expansion offers too litle for me.
Anyway, thanks for help!