Celebrim
Legend
(I'm really curious how people would define the "heavyness" of OD&D, 1e, 2e, 3e, 4e and 5e to be honest - it strikes me that they're all weighted (if you'll pardon the pun) in different directions, so it's not as simple a question as it might appear)
OD&D: Light
1e: Heavy, but with significant gaps in rules coverage compared to a modern rules set, leading to periods that could be described as 'rules light'.
BECMI: Light-ish. Not a true rules light system IMO (I'm not sure a Vancian magic system ever can be, since each spell is a rule set), but very close to being one.
2e: Heavy, but slightly less so than 1e, merging in some of BECMI's simplicity. Conversely, 2e begins the process of extending rules coverage.
3e: Heavy. Very mainstream attempt at a generic universal rules simulation, comparatively slimed down to fit with AD&D's mix of abstraction and process simulation.
4e: Heavy. Design feels abashed to me, with the most successful GMs seeming to take the game in directions that are not explicit in the text and tend to make the game more rules light.
5e: ???