Thanks so much! Shame to hear that it's falling apart, not looking forward to the idea of long bus journeys! Do you know if there are any international lines? Thinking of heading out from Zagreb to see Serbia, Montenegro, Bosnia & Herz etc, and was hoping to do it by train, but it's not sounding hopeful! Also, I saw that there was a train from Zagreb to Zurich - is this true?
There are a few through trains to Zagreb, running via the Tauern and Karawanken tunnels and Ljubljana, and day and/or night trains to Vienna, Budapest and Belgrade.
The Zagreb-Belgrade day train is actually posted to start overnight from Zurich, with coaches added at places like Schwarzach and Villach, but on the day I travelled (June), the entire train was taken out of service on arrival at Zagreb and a couple of fresh coaches appeared to form the day train to Belgrade.
They tried to detach one of these at Vinkovci, but as there was no hope of shoehorning everybody in to one Serbian coach, they relented and 2 coaches went on to Belgrade.
After a day without refreshments, we were astonished that a travelling ice-cream man appeared on the train in Serbia which improved the last lap no end.
Novska-Vinkovci (a long stretch of double track along the Sava) has been refurbished and seemed quite good at about 120km/h (75mph).
Zagreb-Dugo Selo, which is the junction for Budapest, has similarly been upgraded.
But Dugo Selo-Novska is still an old single track at no better than 80km/h with many local stops.
The stretch in Serbia is double track but in poor shape.
You also get the double HR/RS border checks, and they are thorough.
Beware the Belgrade train now uses the new Centar station in Belgrade, now the original station has closed.
The HR/SI border at Dobova is manned by both EU states so you get checked in quick succession while they change the loco (3kV DC to 25kV AC).
You can get some idea of train formations here:
https://www.vagonweb.cz/razeni/vlak.php?zeme=CD&cislo=172&rok=2012&lang=en
HŽPP also has some nice modern Desiro trains for branch lines, but they are infrequent and desperately slow.
Gradually, lines damaged in the war are being brought back into service and refurbished.
The routes to Vienna (via Slovenia and Graz) and Budapest are due for upgrade in both countries.
All I can say about the trains is that they are better than those of Romania and Bulgaria.
Bosnia has some new Talgo trains sitting idle because the two entities and HR can't agree with each other on operational matters.
They were intended for a Sarajevo-Banja Luka-Zagreb service, but now do at least run Sarajevo-Mostar within Bosnia.
Montenegro (Podgorica, Bar) can be accessed from Belgrade on day/night trains.
I was amused to find that the Serbian locos on my trains to/from Belgrade had manufacturer plates showing they were built in Zagreb in JŽ days!
On ownership, I think all HR's track/trains are government owned, but there is considerable interest from China and Russia in all the Balkan networks.
Russia is upgrading routes in Serbia, and there is a large Chinese investment in the Belgrade-Subotica-Budapest upgrade.
I think Russia has taken over operation of the infrastructure in Bulgaria.