Let me put it to you this way:
I'm not the world's best gamer. Playing on easy, three full games and a little grinding have gotten me an 850 out of 1000. The only non-difficulty related achievement I have left to do is complete the challenges (only challenge #14 remaining).
I'm even seriously considering going after the difficulty based achievements (for the full 1000) which I normally wouldn't even consider (again, not that good a gamer). If *I* found this game shockingly easy, someone with more skill should find it a breeze.