I play Nasus pretty regularly, and I do ok with him. I think a lot of the problems and confusion around Nasus are best explained in this post from the "High ELO Nasus question"
Mehacton's post sums it up:
"I think much of the problems surrounding Nasus are caused by the inherent universality present in his skill set - put a different way, he can do it all and so there's really little clue as to what one should do. Unlike, say, Ashe (who is generally restricted to DPS) or Amumu (who is generally restricted to tank), Nasus can do both well and occasionally simultaneously.
In that light, I'm not completely sure that there is a single "high ELO Nasus strategy" that can be repeated verbatim and copied. Lack of a direct advantage, like high base damage or a significant disable, is a bad thing at these early stages of the game when individual heroes haven't yet become fully empowered, Nasus foremost among them. Siphoning Strike is weak as one hasn't had time to feed it, Wither's full slowing effect is nice but seemingly ineffective against caster heroes, and Spirit Fire is okay.
Nasus is a character that tends to scale very well the longer the game goes on. Two of his abilities (Siphoning Strike and the ultimate) become stronger as the game wears on, while Wither's percentage-based slow becomes even more significant. The only static damage spell he possesses is Spirit Fire, evne his passive ability is percentage-oriented. I think this explains the philosophy behind the item builds discussed here quite nicely - the quick tanking items allow Nasus to become "a factor" much sooner than he normally would. Later on I imagine these would be replaced by other, more beefy tank items if the game should last that long.
It's worth pointing out that this is essentially the opposite of most heroes - rather than using skills to get good items right away, Nasus is content with using okay items to wait until his skills power up. I think this inherent strategical dichotomy between Nasus and everyone else plays some role in the difficulty of the character.