My favourite game, all categories. Endless hours of gameplay, and you can play it on almost anything!
The downside is the games are typically pinned to an exact nightly build. I got tired of that, but it's managable for a finite duration to get you started.
Turn off vehicles breakdowns, and there's setting to change towns to follow 2x2 or 3x3 grid, which will make building easier.
To make early money, look for two cities (they have City label on their name) with high enough population and close enough distance, and make 7 length station on both. You'll want to run 7 length on every passenger train in the end, it'll simplify the design.
The ui and menus may be confusing at first, but you'll get used to it.
I like Simutrans [0], in which people want to get from A to B and are willing to change between bus/train/plane. The routes which are central to one's network really need to be able to bear a lot of passengers.
There were attempts to introduce more simutrans-esque behaviour in patches called cargodest, but it proved to be unacceptable performance wise for the map and network sizes that OpenTTD uses.
And without cargodest, what is the point of OpenTTD? I honestly struggle to understand this game if passengers appear randomly and pay the full price to go wherever you like to take them.
It's probably also worth mentioning that cargo quantities are usually more limited at first. Primary cargo especially grows slowly. Passengers can grow very quickly if the player understands the city growth mechanics (the count is a function of city size), but even with cargodist if you make an actual network they will dictate their stop.
For me the appeal is more the mid-late game micro-optimisations, like how to make a junction work when there's constant incoming trains.