What is wrong with the classes?
I'm not gonna be giving an opinion in the subject rather than explaining why they have a polarising opinion on them.
This goes beyond this game and the genre. This can apply to MOBAS, FPS, fighting games, etc. A unit/ability which requires perfect input to do well, high risk/high reward, a really specific style of playing to counter, feels UNINTERACTIVE.
The one on the receiving end feels "cheated", while the one who's using it argues that his effort should be rewarded if not it's pointless to even try to use it. Then the game revolves around been able to counter the unit before it deals to enough damage.
If it's only from a watcher's perspective, this kind of things tends to be "exciting" as the results and influence of the units/abilities tend to be clear in what they achieve.
How this correlates to CoH?
In vCoH it was all about the sniper duels. Snipers who could cloak whenever they want and most of the time, the best counter to them is another sniper.
vCoH2 had snipers with less powerful cloak and they went with the assymetric route (at first) to remove the whole sniper vs sniper duels. The 2 new factions introduced some year later didn't receive any sniper at all and instead they got units which could crit (1 shot kill) if the model they were hitting were low enough in HP. People who hate snipers prefer this type of marksman squad.