What I hated was not usually considered by players.
I've been, and I'm still, a developer for a player-based UO shard. So how the game engine runs for any game is pretty important to me... and I found that the CoH "success engine" was horrendous. The problem was that it deals with modifiers linearly (+5 Defense means literally a +5% to your Defense in a linear percentage-based formula), which makes adding more and more Defense (or Resist) more effective than the previous point of Defense or Resist. Until you reach the cap, and then the newly added point becomes completely useless (except for protecting against debuffing).
It really should have been coded with a curved function, that asymptotically curves towards the cap (95% maximum chance to hit, for example). That would allow for several benefits:
1) Adding more and more buffs to a stat becomes less and less effective because the slope of the curve changes so you're getting less benefit. This instantly and automatically replaces ED, and we would never have needed the ED nerf.
2) You can never cap out. I never liked the concept of being capped. However, that allows you to get benefit from multiple sources of buffs without having the additional source "wasted". As we all know, you can't add a 2nd Kinetic in a large high level team and get much use from them, since it only takes one Fulcrum Shift to cap the entire team's +Damage (except maybe with Brutes). Similarly, a 2nd FF Defender in a team is nearly useless unless the opponents debuff Defense. But if you can't cap out, then the 2nd Kinetic and the 2nd FF always adds more to the relevant stats, even if it's not nearly as much as the first.
3) Because of the diminishing effect of stacking buffs and enhancements, we don't need any actual caps. The asymptote of the function's curve acts as an actual cap, so we don't need to artificially prevent players from adding more enhancements or buffs to any ability.
If they did that from the beginning of CoH's design, it would have prevented a LOT of issues from happening. I really hope that they go in this direction with CoH 2.