Advtrains is the kind of mod that has twofold appeal: From the perspective of people who will never learn its ins-and-outs, and from those who will learn all about the mod and enjoy its richness. It's the definitive method of public transport for Minetest - even the boats and buses of linetrack are based on this core, and teleports can't compare. The way all trains are always operating, even through unloaded areas, is just the beginning of its rich features.
The track system is first class among railway mods for block games, with 30 degree increments, slopes, 45 degree slopes, diamond crossings. No limitations on placement. It's still not 'realistic' but it leaves minecart tracks looking janky.
The signalling and interlocking system has profound depth, though at cost of complexity and being notoriously hard to learn. If you're a lover of signals, this goes beyond OpenTTD or Factorio. Save yourself some trouble and ask other players for help learning.
The trains can also carry your cargo. Moving stuff by train is great fun, better than any other way I can think of. Challenge yourself to build a realistic freight railway, and then sit back and enjoy automatic operation.
Don't like driving? Need to run a timetable? Want something even more elaborate? Start with basic ATC tracks and station/stop rails, and later discover how automation and full control is always available through Advtrains' Lua environment "LuaATC" for anything the train can do.
I have to admit Advtrains' faults: It's hard to learn, it can lag your server badly (the more trains the merrier.. er.. laggier) and one misstep with LuaATC can crash the server. The selection of trains is growing but still not that broad across people/goods, city/country, nationality. It's not super survival friendly. Waiting around at a station for a train to come is probably even less fun in a video game than real life. But I just can't name anything that gives you this much control of computer game trains!