the other economy that appears to be fairly interesting to understand (but not necessarily to partake in) could be EVE Online. Because I only have a few unscheduled hours of free time a week to play video games, I haven't been able to get into it. Eve is one of the rare MMOs to allow two-way markets which presents plenty of opportunities for traditional market making. As far as I can tell, pure arb is hard to come by given all the fees and most mkt mkrs make money taking a combination of inventory, production and transport risk. now if Eve standardizes chartering freight the economy will get closer to how commerce works in the real world, but as of now these activities feel a little disjointed.
as for the other MMOs, i feel they are a little bit on rails. games like WoW and PoE allow all kinds of low-risk "arbitrage" because of the lack of a two-way market. i played wow for a while and i found it's not much of a rush to snipe ignorant listings as acquiring 1000s of g in raid materials to craft raid level gear that sell for multiples, just from the tremendous risk being undertaken. the best guild traders were not merely trading on the auction house, they had Top-of-Orderbook relationships with "Chinese farmers" and they'd craft discounted raid level materials into equipment and potions to sell to new guilds getting into the heavily-gated raid scene (this was back in 2004-2008 when i was active), so that these new guilds may one day have their best tanks poached by the very same guild that got them started in the first place.
i played wow just before my college days when i was all ready to make an education and career choice for the rest of my life. i was all set on EEE but at the last minute switched out (to math/econs) when i realized i hadn't been merely playing video games in the same way this person hadn't just been playing minecraft.