I'm going to get crucified for this but here it is anyway:
I liked the sub rule.
It meant that if one team lost a player to injury, they could sub them off without losing an active spot on the interchange bench, hence giving the opposition team less of an advantage.
Without it, one team can be reduced to three fit players on the interchange bench while the other still has four who can be rotated freely.
Don't understand why people were so heavily opposed to it, I was sad to see it go. Injuries now have a bigger impact on results, when they don't need to.
I can see the benefits of it, but it meant if you got more than one injury it was a real problem when the opposition injected fresh legs towards the end of the game. Plus almost every sub was a smaller player and when ruckmen or key position players went down, the same problem was encountered by teams.
With midfields made up of 8-10 rotating players, adding one more into the mix later in the game wasn't really that important.
I think my unpopular opinion is that losing just one rotation through the midfield is not that important, some teams have less players rotating through anyway. I think the whole rotations thing is a bit of a myth that the club with more rotations would have fresher legs. I think confident winning teams rotate more while worse teams rotate less (have less decent players to rotate) so the statistics would skew to look as if more rotations equalled more success, when it was the other way around.
When Hawthorn were 10 goals up they could afford to rotate Sam Mitchell and Luke Hodge off the ground. When Essendon are 2 goals behind, they're hardly going to rotate off Watson (in his prime years) for a first or second year player very often.