Diablo 2's Runewords are Being Resurrected in Diablo 4: Vessel of Hatred

ign.com:

During their livestream today, Blizzard announced a rather unexpected feature will be returning to Diablo 4 with Vessel of Hatred: Runewords.

Found exclusively in Diablo 2 up until this point, Runewords are an upgrade system that lets you imprint your equipment with special properties by combining specific runes to form words with potent effects. Though Diablo 4's take on this mechanic has been overhauled, the fundamentals remain the same, and will offer an entirely new way for players to power up their heroes of Sanctuary.

In an interview with IGN, Diablo 4: Vessel of Hatred game director Brent Gibson explained, "The biggest change is that the requirement is sockets. The D2 system is great, but it's also not super approachable for the larger audience. We wanted to have a really great system that made it easy for you to socket, basically an 'IF' statement, then a 'THEN' result. So as long as you have two sockets in your gear, you can place two different types of stones. You have the ritual stone, which is the condition, like 'on potion,' and then you have the invocation stone which is the power that's cast, like 'earthquake.' So every time I use a potion, cast earthquake."

Owing to Diablo 4's socket limitations, Runewords will rely exclusively on this IF/THEN system and will do away with the much more complicated version found in Diablo 2 where Runewords could involve up to six runes on a single piece of equipment. However, the flipside is that there will be fewer limitations on what kinds of gear can have Runewords imprinted on them and there will now be different rarities of runes to chase, including legendary runes that will have a major impact on gameplay. One example of this is a invocation rune that can add the sorcerer's teleport ability to any character whenever it's triggered.

"Teleport, for example: Here we have the Spiritborn. You spec Jaguar and Eagle -- you're already all over the place, plus you add teleport on top of basics? Like, holy s**t! Untouchable!"