Graphics are important, however they are no more important than the gameplay. In the end what it all boils down to is whether you are able to play it. If it has awesome graphics, but plays like shit, then I probably would cast the game aside immediately. This question of playability however also applies to graphics as graphics do provide the player with a sense of immersion.
Let's be honest, playing a shooter set around present day (or world war 2 for that matter) with minecraft graphics wouldn't give you the same sensation as when you can see every detail of the face of that enemy soldier you just peppered with SMG rounds. The realistic graphics make you feel as if you yourself are in that game, because it is hard to tell the difference between reality and the game (well not quite, yet. But you know what I'm getting at).