I got irritated with Open TTD because they made a change which broke the game for me.
They made it so that industries can close down for what seems like arbitrary reasons.
I used to edit the scenario before I played it, and add extra industries in places that would make me more money. So, as an example, I'd place 6 coal mines at one end of the map, and then a power station at the other. This allowed to me create a very profitable route because the 6 coal mines kept supplying enough coal to completely fill a train, and the long distances involved meant the payoff was enormous.
The problem was, with these changes that they made, pretty soon those coal mines would start closing down, and then the route would not be so profitable anymore.
I don't care that it wasn't realistic or made the game too easy - I wanted to play the game the way that I wanted to play it, and it was possible in previous versions of OpenTTD, but then they changed it!