if it goes where you want to, it’s great, nice modern central european trains. Don’t think it’s got the widest coverage though - you can get to the caves on the train from Ljubljana easily enough, but I think Bohinj needs bus or car.
We loved going up the castle in Bled and having a drink looking out over the lake, but the town itself didn’t look appealing. Logarska Dolina was amazing, but probably only possible if renting a car (pretty cheap and roads are great if you stay out of the mountains). Celica hostel and the nearby ex-squat complex (bunch of hipster bars and clubs when we went) was really good fun in Ljubljana, and the centre is really nice to walk around, particularly drinks by the old riverfront. We went for my 30th birthday, so stayed in Otocec castle for a night, which was amazing - old castle on its own island in a river, fantastic food and drink, natural spa nearby.