Only a Slovenian can tell you this, I'm afraid

Even we in the Balkans don't follow them.
All I can tell you is that psychologically the Slovenians are traditionally the strongest of all Balkan people. Mentality wise they're much more Germans than Balkans.
Organization and discipline are their strongest points in everything they do, not only in football but in life in general.
I already said few weeks ago that they're the least talented nation for football among the Balkans (not only the ex-Yu, but the entire Balkan) but still they made it to the Euro 2000, World Cup 2002 and they made it to the play-offs for the EURO 2004 where they were eliminated by Croatia. Now they made it again to the WC.
In 9 years, with 2-3 different generations of players, they made it to 3 big competitions and once they almost made it to another big competition.
If I ask any of you here to name me more than 2 Slovenian players who played at big tournaments or who now play for Slovenia, then Handanovic and Zahovic are probably the only ones you can name.
Teams like Bosnia, Macedonia, Montenegro had more well known players and yet they never made it to play offs (except Bosnia this time).
The Serbs, with many football stars, made it only to 2 tournaments in these last 9 years and this will be their third, just like Slovenia. Croatia made it to 4 tournaments, which is just a little better than Slovenia. Bulgaria made it to to only 1 big tournament, Greece made it to 2 and this is their third. Romania played at 2, Turkey at 3.
You get what I want to say
You can expect great organization and discipline from the Slovenians. That worked for them so far. They proved to be colder and mentally stronger even from the usually cold and mentally strong Russians. But when they'll be against much better teams, from world's top 10, the organization, team work and discipline won't help them much.