OpenTTD graphics are just not even remotely comparable. It looked so ugly when I tried it that I couldn't bother to continue for more than 2 minutes. If graphics don't matter then maybe even drop openttd and play a text based graphic game. It will run smooth even on a raspberry pi.
The game is originally from 1994, what do you expect? We didn't even have 3dfx 3d accelerator cards back then. OpenTTD will run smooth on a Pi. It ran smooth on my 486 when it first came out.
I'm not a huge gamer, but I did spend 14 hours a day for a week playing this game once. Never been sucked in to a game like this. And even better if you can find the original music and graphics. The music is excellent, and will play in your dreams.
First time I played Transport Tycoon was on my 486, I got a demo of the original game on a floppy disk out of some PC game magazine. Looking back, it's amazing how much game play fit onto a 1.44MB floppy disk. I ended up purchasing the Deluxe version on a CDROM. I ripped the CD and have kept an image of it ever since, which came in handy when I found OpenTTD and wanted to use the original graphics and content. Chris Sawyer and the OpenTTD devs are legendary in my mind.