Beyond the Wall (ably described above) and Worlds Without Number are at the top of my list, with Shadowdark in third place a bit behind.
Mechanically, BtW and WWN do a lot of things similarly, boiling things down to three basic classes -- Warrior, Expert/Rogue and Mage -- then allowing PCs to mix 2 of the 3 together as half-classes to cover a lot of additional ground. I like the implementation of skills in both (BtW is roll-under the appropriate attribute, modified by skill levels, while WWN uses 2d6+modifiers vs. a target number). Both include tons of adventure and setting generators. WWN has slightly more crunch but both avoid the HP bloat and bad math of 5E. The main difference between the two is tone -- I find BtW works best for "hearth fantasy" and more traditional, Tolkien-esque hero's journey games, while WWN is better-suited to grittier games that eventually reach higher levels of power.
Shadowdark is more familiar and approachable to 5E players, I find. It has great vibes but the random nature of advancement will be a feature for some and a bug for others. I like it, sometimes, but the comparative lack of control over advancement sends me to other systems for longer or more involved campaigns.
I've been on a nostalgia trip recently going through old 2E campaign box sets, and my preferred system varies with each one:
Dragonlance, Greyhawk or old-school Forgotten Realms: Beyond the Wall
Dark Sun, Al-Qadim or Planescape: Worlds Without Number
Ravenloft: Shadowdark
Mechanically, BtW and WWN do a lot of things similarly, boiling things down to three basic classes -- Warrior, Expert/Rogue and Mage -- then allowing PCs to mix 2 of the 3 together as half-classes to cover a lot of additional ground. I like the implementation of skills in both (BtW is roll-under the appropriate attribute, modified by skill levels, while WWN uses 2d6+modifiers vs. a target number). Both include tons of adventure and setting generators. WWN has slightly more crunch but both avoid the HP bloat and bad math of 5E. The main difference between the two is tone -- I find BtW works best for "hearth fantasy" and more traditional, Tolkien-esque hero's journey games, while WWN is better-suited to grittier games that eventually reach higher levels of power.
Shadowdark is more familiar and approachable to 5E players, I find. It has great vibes but the random nature of advancement will be a feature for some and a bug for others. I like it, sometimes, but the comparative lack of control over advancement sends me to other systems for longer or more involved campaigns.
I've been on a nostalgia trip recently going through old 2E campaign box sets, and my preferred system varies with each one:
Dragonlance, Greyhawk or old-school Forgotten Realms: Beyond the Wall
Dark Sun, Al-Qadim or Planescape: Worlds Without Number
Ravenloft: Shadowdark
