It's not perfect, but it levels the playing field a lot more than other systems. And it's good at making sure talented but poor students have access to the best programs. At those the level is high, for example the best math program probably has the highest Fields medal per student ratio of any university in the world.
The downside is that universities and engineering schools are small and underfunded so they don't stand out in worldwide rankings.
How do rich people game the system? They can to some extent game it earlier, putting their kids in better high schools. But the kids will still have to take the same exams. So generally they just avoid this system and put their kids into business schools, which are not state funded and where admission is based on much softer and game-able criteria. Or they send them to US universities.