My daughter was there a few months ago and I can report that passenger trains are SEVERELY restricted - pretty much the only place you can go is back to Beograd.
She had to uses buses which were infrequent but serviceable although the roads were generally appalling and a journey (Podgorica to the Croatian border) which would have taken about an hour in any EU country you care to pick at random took 2.5hrs. Fares were low (compared to EU norms) but you get what you pay for.
MNE needs to rapidly and massively upgrade its transport infrastructure if it wants to be taken seriously as a tourist destination for anyone other than a few rich russians. It's hard to get TO, it's hard to get AROUND, and it's hard to get OUT. I know there are mountains - but Switzerland, Italy and Austria have mountains too (that's what engineers are for) ... and in case some think it's a question of MONEY then please note that Bulgaria, Romania, Slovakia etc have mountains ... and their rail system works just fine. Why does the Niksic/Tirana line ONLY take freight? How much extra money would it cost to upgrade it to a freight AND passenger line?
Also, note how difficult it is (with the exception of Beograd) to travel from the MNE capital city to the capital city of your nearest neighbours. Trains to Zagreb, Sarajevo, Tirana, or Pristina? forget it. So MNE is disadvantaged for tourism AND trade.
Can you imagine a Frenchman being told that there is no train to Brussels, Berlin, Geneva, Madrid or Rome? He'd laugh in your face and the entire Board of SNCF would be anticipating unemployment