The Casual stuff brought me back.
I was anti-WoW for a while, you can check my post history.
I picked it up again recently, friend let me use her account and now that it got hacked I'm going to pick it up and get my own account.
I leveled a DK to 80 because I did 6 of the original vanilla jobs to 60 before BC and wanted to try something new.
First - 10-man/Heroic 5-man. The deal is the same as doing UBRS or the like back in the old days, except the gear has been itemized to allow you access to the hard stuff. It's a great job by Blizzard because only being able to do end-game content if you were in a 40-man guild was very discouraging and didn't allow you to act without consequence. You had to walk on egg shells or you'd get "blacklisted" by raiding guilds. Now? Say whatever you want, because you can get epic gear in pugs.
Second - PVP. It's so dimensional now. There's arenas, big area/zones like Wintergrasp, gear rewards/mounts. It's crazy, the competition is so high. People say it killed world PVP, but world PVP sucked. The only people who enjoyed it were people who liked ganking lower level players or doing nothing with their time. It served no purpose and people never went anywhere with it. You'd start out at Crossroads or Southshore, you start winning, you try to sack Undercity or Orgrimmar/Iron Forge but people stop following you because of how long of a run it is or you get picked off or the sheer amount of opposing faction come in and destroy you, it falls apart.
Zoned/controlled PVP makes sure the fight is interesting enough for people to get into it.
The emblem/recruit a friend/heirloom system is fantastic. Right now I'm going to get 300% for leveling with the person who recruited me, on top of that, when I hit 80 with one toon, I can send heirloom gear to my alts. Basically gear that levels with you and remains as good as "good blues" your level. At level 80, a 2h axe has the max dmg and DPS of a level 80 heroic blue. But you never have to upgrade it. You can keep it on you from level 1-80. The same for the shoulders you get, but they also give you a 10% bonus experience buff.
Blizzard also increased the quested XP you get in pre-BC.
Also, go to Wow-pro and get Jame's alliance in-game guide. I just barely started using it, but I can tell already, this mod will get me past the boring 1-60 levels super fast.