Care to elaborate on why you think this? I just watched his last fight, and I saw some qualities but not enough to suggest to me he is a World Beater. Clearly hits very hard, and commits to all of his punches, but not a lot of emphasis on defense, and this saw him being tagged with the jab and the odd power shot. I didn't see much in terms of punch variety either, he was straight up and down.
Because he is clearly world class as the MW division goes (Martinez is a cut above any) and if he was a euro-level gatekeeper then he would not be.
...This doesn't really answer my question. What qualities do you see in Golovkin that suggest to you that he is a potential world class fighter?
That wasn't your exact question.. but anyway. World class is down to the era of the division and right now Martinez a cut above, with 'world class' probably being defined as people like Pirog, Sturm etc; by popular opinion. He has rounded fundamentals from a good amateur career and genuine power, therefore parts of a fighters make-up that match-up with those of Pirog and Sturm on the h2h stakes. I like his timing and quick feet also.
I wouldn't have guessed Golovkin enjoyed an extensive amateur career from watching him fight. He's sloppy, and like I said before, he doesn't seem to have a lot of variety in his punch selection. He looks like a banger, he didn't demonstrate an educated jab, and he wasn't setting up any of his shots. At least this was the case in his last fight. You think power is enough to win the day at 160lbs?
Enough to be considered world class at 160 combined with his quick feet, timing and the fact his skills in every other area are better than that of 95% of other middleweights.
Golovkin seems to be as basic at they come and indeed does have some very impressive wins over very good pros in the amateurs. He reminds me abit of Forrest where Golovkin doesn't have a flashy style, but does enough to win and his power is very effective. Now all he needs is a world class trainer to get to that higher level. He is lacking greatly in hand speed and defense, but is a rare case where he has faster feet than hands like someone else mentioned, so he's in always in good position to land that wicked right hand of his.