I've had my '04 GTI since it was new and I've just ticked over the 80k mark (this is my second GTI, after a '02 Tiptronic). It has never once had a mechanical or electrical problem. I've done just about everything in it...5 people and their stuff, track days, commuting, long road trips, backroad drives, snow, rain, sun, traffic, moving...short of towing or off-roading there's nothing it doesn't do competently or better. It's such a delightfully well-built car, it's no surprise that VW didn't actually profit from the MkIV Golf. Yes maintenance is important, but isn't it with every car? Do it on schedule and it's unbeatable!
Great space inside and compact outside, styling is aging well inside and out, interior ergonomics are great, headroom and legroom are great (rear legroom is good for a small car, fits real adults!), gutsy power from pretty much anywhere on the tach, grippy chassis, hugely knowledgeable and well-developed aftermarket and enthusiast base (no question unanswered, no part unmodifiable :) ), great paint quality, good stereo. I'm glad I skipped the sunroof.
In terms of steering quickness, suspension stiffness, bushings, braking capacity...honestly it's about 20% shy all around from where I'd like it. Fortunately the aftermarket is so well developed that you can go through it and turn everything up a couple notches, which is what I'm working on! The mileage (24/30 for me in real driving, 27-28 average) is good but IS starting to look a little low compared to the MY13 cars. Stereo is light on bass (but sounds good otherwise). Wish the seating position was a little lower. While I'm dreaming, popout venting rear windows à la 3-series coupe (with only two windows, it doesn't vent that well). Stronger A/C (gets very cold EVENTUALLY)