....but is it? I've got an enormous map...and I'm not able to get to every room. I get abilities which let me explore a bit further and then I'm stuck again on that part of the map ... but wasn't there that one room for which I got the relic a few minutes ago?

THAT's my interpretation of a MetroidVania ... does it play like that?

It's more like this one:
Mazes of Galious remake

Which in fact belongs to the Metroidvana genre ;)

Well yes... ;p but I don't think it has some of the keys features of the "genre"..

But I also mentioned that game, because it was the direct inspiration for UNepic. (or at least is what the developer says... ;p)

Stop calling everything metroidvania, call it metroidkiller.
None of those games had treasure to find

Wrong, the first Metroid was released in 1987, just as Maze of Galious, so they are sort of 'independent'.
And excuse me, comparing this to Metroid games... Silly. From the Wiki:

... The Metroid series contains gameplay elements from shooter, platformer, and adventure games.[1] The series is notable for its non-linear progression and solitary exploration format where the player only controls Samus Aran, with few or no other characters to interact with. The series has been a 2D side-scroller in all its incarnations until the ...

Clearly Unepic takes a lot from Maze of Galious, just moves it much further, game evolution. :)

I never compared them...
I could now explain the difference between a game and a genre...but i won't.

Unepic can loosely fall into the metroidvania genre I would say. Metroidvania isn't really a genre, in the same way that rogue-like isn't really a genre - more of a descriptive way of seeing some similarities between games. (I don't think it's really relevant to argue that Maze of Gallous can't be a metroidvania because the term hadn't been coined yet)

Unepic has a single world map with a lot of backtracking, and is viewed from the side. It also has experience and other rpg elements like the castlevania games do.

On the other hand, traversing the map has more to do with finding keys than expanding your movement abilities, and doesn't really feel that similar during moment to moment gameplay to other metroidvanias.

So make your own decision if it really should be categorized as such or not :)

I don't fit Maze of Galious in the Metroidvania category, simply because, for me, a "real" metroidvania must have item-based progression, as in, certain parts of the map are locked until you have the right item or skill to reach them. MoG doesn't have that, unless you count the keys to open the different doors for the bosses; but that is only a way to keep some linear stages mixed in with the open-world map, can't really be considered "item-based progression". Again, I must stress, this is the most important characteristic that makes a game "metroidvania" FOR ME; your mileage may vary.

That said, if Unepic takes its inspiration more from MoG than from Metroid (I've only just started playing, but it certainly looks like it's the case), then it makes it not-exactly-metroidvania in my eyes. Still a very good game as far as I've played, though. I say buy it, you won't regret. :)

EDIT: I should just have written "what Saluk said" LOL.

Whatever its genre, Unepic is wicked cool. There should be more exploration games that don't dick players over.

I never played Maze of Gallious.

The handful of games I remember on the NES that I vaguely remember feeling somewhat similar or having side scrolling progression/ adventure and exploration include Metroid, Casltevania II, Faxanadu, I think one known as Legacy,of the Wizard. My aunt had the latter 2, I never actually ever got that far.

http://www.telebunny.net/toastywiki/index.php/Games/Metroidvania09Faxanadu

Faxanadu though is a game I always wished they'd make a remake for, it definitely looks worth beating. I don't remember enough about Legacy of the Wizard other than the iconic room with the dragon in it.

http://www.vgmuseum.com/mrp/multi/Essays/essay-squalidpumpkin5.htm

Maybe I saw or played a few others on the list but I barely remember them, or what made them similar to metroid or Castlevania II.

Have you ever played "Symphony of the Night"? Few games have more treasure and legendary items, than it...

Few decent games have worse game balance than it.

You are asking the wrong question.The right question is ''Does it feel good to play?''.
The answer is yes no matter how you call this game.I've seen people call it The 2D Dark Souls.If this helps.