1. Elitism: you can't find a group that will take you with them, if you haven't have enough "LI" and "KP" (so much for casual players).
2. Trainings: what fun is it to have to train for certain content in order to qualify for the real experience?? No other game mode does that. Sure, the more often you play a certain content, the more routine you show. But to assume a player cannot get it right (with some directions from the "pros") the first time around is offending one's intellect and skill.
3. "Save Points": you rarely find a group that does a raid wing from A to Z. It's always a certain boss being named in LFG. Who made up this "save point" design so that people don't have to play through a whole wing in one go? (I miss the good ol' GW1 FoW/UW elite instance days.)
It's just frustrating. Today, I was really in the mood to raid again for a change (haven't in ages because of said design), as I wanted to go back to the Unterworld and meet Dhuum again, but was quickly reminded why I had quit in the first place (because not being accepted into any group due to my low LI and KP stinks, and seeing the same bosses like the Vale Guardian or Gorseval over and over again and never experiencing a full raid just gets boring as hell quickly).
Please, do something about your raid design, ANet!