For those not possessed of their own copy, EPT is quite clearly an OD&D variant and a pre-Supplement I variant at that. There are only three character classes (warriors, priests, and magic-users), hit dice and damage are all D6-based, and armor class goes from 9 down to 1. The OD&D pedigree is quite apparent, even with only a cursory review of the game rules.
However, EPT is nevertheless its own game, as there are dozens of little changes, tweaks, and alterations to the basic OD&D template. It's these I find fascinating and I keep coming back to. Just a few examples:
- Spell level is not as rigidly tied to the level of the caster. That is, a 2nd-level priest can choose whether to try and learn a spell of "appropriate" level or take a chance and learn a higher-level spell instead.
- After level 3 (or Level III, as EPT puts it), all XP gains are halved. At level 10 and up, a character earns only 5% of the normal XP accrued.
- Attackers with higher hit dice than their opponents roll more dice to determine damage, with damage that exceeds the hit points of an opponent being applied to nearby targets.
To me, that's how all RPG campaigns should be. It's certainly something I strive for in my Dwimmermount campaign and it's what I find most intriguing about tales of the old days. Even in 1980, shortly after I was initiated into the hobby, it was still a given that, when playing in someone else's campaign, there was no guarantee the referee used the same rules or interpreted them the same way that you did. Each campaign was its own little world and it was folly to assume each operated under the same "physical laws." Re-reading Empire of the Petal Throne is a good reminder of this fact.