Nothing at all.
Well where to begin?
This is a simply awesome car in every way you think a car should be; handling, brakes, performance, comfort and styling are all top notch.
Had the car for about 15,000ks, and it hasn't missed a beat.
Servicing is quite expensive, but I would still recommend using a Skyline specific servicer for major things you can't do yourself.
Built quality is very good coming from a conformadore :P
Heading up the twisty mountains or cruising beachfront is what this car was made for. It is fairly fast; if you're the sort of person that likes the traffic light wars, it will pwn nine out of 10 cars that you want it to.
Mods are readily available, but expensive if you're doing them from scratch. If you want a stocky, keep it that way IMO. With a new FMIC, turbo back exhaust and bump the boost to say 10 pounds, you'll be pushing 200rwkw.
Actually not that bad on petrol; I get 550kms/tank of reasonably hard driving. Although keep the tacho above 4,000 and watch the petrol gauge have a conniption :)
So in closing, a highly recommended import that is thankfully very affordable now ($12k-$18k depending on mods, year), and if you treat it with a little respect, it should provide many years of motoring enjoyment.
I own an 1996 R33 GTST, city driving it does 350km to a tank. Maybe 500 freeway. Completely stock and makes 157kw at the wheels.. how in hell can you be getting 550...
Using premium and having it tuned to do so.
I have 220 RWKW in mine and get 400+ out of the tank. Usually average 11 per 100km. With mixed driving. Don't expect any less that's for sure.
As others have said, if you can't afford it, get a Civic or Corolla, but if you want POWER, you have to pay for it. :) I have and am loving it. Others cars I owned don't compare to it. (Honda Integra, Ford Probe, Rav4, Nissan Pulsar, Mazda 626, Honda Accord).
Fun car, with plenty of ballex.