Were all the mechanic 1 checks the same in terms of whether you wanted to roll high or low? Were there ability checks? Just interested to know from a game history point of view, as I came in several years after OD&D and have never played.
Yes, all of the "mechanic 1" and "mechanic 1a" checks (attacks, saving throws, and turn undead) are roll high.
There is no official ability check mechanic described in the rules. However, it's worth pointing out that OD&D assumed a more "free" adjudication paradigm as opposed to the more "strict" adjudication paradigm that D&D has shifted towards since then.
By "free" adjudication paradigm, I mean that OD&D utilized a method of judging based on the "free kriegsspiel" model of miniatures wargaming as opposed to the "strict kriegsspiel" model.
https://en.wikipedia.org/wiki/Kriegsspiel_(wargame)
Nothing terribly simple about the use of attack and saving throw matrices, though 0D&D 'before supplements' was a period of what, a year maybe, before Greyhawk came out and moved the game away from using Chainmail for Combat, and introduced the Thief with it's % skills. IDK how simple using the Chainmail wargame for combat and Avalon Hill's Wilderness Survival for exploration may have been, heck, I've only heard rumors about the latter...
Simplicity is a matter of opinion. The OD&D attack matrix for characters is only 8 rows by 6 columns. The matrix for monsters is 8x8. I typed up my own quick reference spreadsheet that I use when I run the game and the two attack matrices, the saving throw matrix, and the turn undead matrix all fit comfortably on one side of one sheet of paper. Those are all the matrices you need for combat.
According to people who played in the original Greyhawk campaign, Gary didn't use Chainmail for personal combat, only mass warfare. The OD&D rules simply state that the referee could opt to use Chainmail or use the new system. This was done partially as a product tie-in for Chainmail and partially as a nod to the fact that Dave Arneson at one point used Chainmail as the basis for combat in his proto-D&D Blackmoor campaign.
OD&D suggests using the Outdoor Survival map as a map for wilderness adventures (i.e. hex-crawling). Given that hex graph paper probably wasn't easy to get back then, it's just a simple alternative to having to draw your own map.
As I stated at the beginning of my original post, I'm talking about OD&D prior to the Greyhawk supplement, so the thief class with its d% skills is outside the scope of what I'm talking about.