Lets's start with the most obvious: Everquest
I played EQ starting from Ruins of Kunark until Gates of Discord, one of my mains was a Shadowknight from Paineel making some of the biggest changes affect me directly.
The original was running one server per zone. While able to cope with a few dozens of players at the same time, lag spikes were widely known to occur in hot zones (as during GM-events).
A few years later SOE showed during a E3 talk (if I remember correctly) a dynamic balancing system in what whole images of zone servers wee balanced on a computing grid. This got rid of the lag and due to the fact that less used zones could share a low-powered host saved them probably a lot of money.
Basically what they invented was one of the first computing clouds as later brought into mainstream by Amazon and Google.
(picture from wired.com)
Again, the original Everquest graphis engine was what we would best describe now as "god-awful". Especially bad performance showed in places with lots of different textures and NPCs (Paineel anyone?). This was mainly due to the client rendering everything and the removing bits you couldn't see from you POV (as of patch notes). Soon later SOE/Verant used a technique mainly in use by NEC during that time to calculate first the POV and THEN render the rest of the environment as needed.
(late alpha screenshot from alkarazham)
SOE brought out a Mac as well as a Playstation version of EQ, and therefore rank as the first multi-platform MMORPG publisher I know of. The various platforms had their own servers and development teams. All of the non-PC versions were/are not too successful.
The Mac version met its final fate in 2004 when the company tasked with the development did it's last patch. Also it didn't help, that the PC expansions usually took months to get ported (in various stages of completeness). But the surviving servers seem to get a few more players from people looking for the "classic" experience.
at least for me, my first encounters with the following happened in EQ
* different drop rates based on level and place (TLC)
* instances (LDON)
* time dependent spawns (switching between lvl 10 to lvl 40 during the night)
* underwater exploration