A need for class trainers is gone - you still can wait that spell. Now you just see it on your spellbook rather than on trainer. Difference is you dont pay for it, which is good thing considering inflation of ingame money and low level greens costing several gold in AH (few silver used to be good price).
Spell tooltips showing you when to use your spells - didnt they always tell you what they did? + rotations are by far more complicated than anything vanilla or TBC offered. At lvl 10 you have more usefull spells for PVE than you had at 60 during vanilla as dps.
Talent trees - you googled right spec. There was one spec you used. If you didnt you were terrible. Oh the excitement getting 1% crit when you leveled... Wait that was boring as hell. At least nowdays most talents are usefull somehow and you can make difference by changing them and glyphs. By far more complicated and far more options than there ever was.
Dungeons - there is challenge modes if you want bit more challenging content. There is also Brawlers guild for solo PVE. Even though i have good memories about spending 5 hours in BRD, it actually wasnt that much fun. I prefer current design over it. It was just messy. Though they could make some options to it like different wings etc. but over all i would consider current one improvement.
Raids - Dont do LFR then. Its for people to see content easily and have some form of gear progression. If you want challenge get to normals or heroic raids. If someone else sees content it doesnt take ANYTHING away from you. Just be happy there is something for everyone.
Vanilla / TBC was just time consuming, not really hard. People were terrible players and most bosses were tank and spank. Bosses were hard because they were enormous gear checks. I loved Vanilla / TBC but i prefer current content.