An opinion that I've seen brought up once or twice in the forums, but which I feel deserves it's own discussion, is that stuns from early game units such as space marine scouts and scrapped-up ork slugga boyz, should not impact late game elites, or even vehicles. An example to illustrate how silly these stuns can sometimes be would be a squad of 'ard boys charging at an imperial knight paladin before it executes a chainsword sweep, stunning and preventing the ability being used. I mean, a dreadnought slam? Fine. Stagger and stun anything you'd like. A basic unit charging and stunning a super-unit? That has problems.
First off, this somewhat ruins the impact of the late game elite when it can be harassed that much by basic usage of an early game unit. Holding off for a 9 or 10 point elite is a huge decision in this game which is largely dominated by early game elite choices. The reward should for holding out should be commensurate, and having these units countered by the same easy stuns that counter your 3-point elites isn't ideal.
Secondly, we already have a precedent for stuns and other effects that act against certain armour types but not others - Ronahn's long shot stuns vehicles, but not infantry. The slow death doctrine for tactical marine flamers slows infantry but causes vehicles to become immobilised. Surely it would be fitting for a scout grenade/'ard boy charge to stun infantry, but not a tank?
Lastly, we can't ignore the feel of play, as it's something many who dislike the game feel is 'off' relative to the first two games. Aside from the ridiculousness of a towering imperial knight stopping mid-chainsword swing because a slugga stood on it's toe, an endgame unit being countered this easily detracts heavily from the feel of how powerful these units are supposed to be. Consider in dow1 a bloodthirster having a crowd control ability countered by an ork slugga. Or in dow2 a hormagaunt cancelling the avatar of khaine's wailing doom ability. The 9 and 10 point elites are the "showstopper" units of this game, and controlling them is something a new player should feel giddy doing. Having them staggered by a unit they are designed to overwhelm, in the middle of an ability designed to counter said unit, ruins this feel. Especially in a game where so few units truly feel durable.