I hit level 75 of Dufe last night.  I figure this is probably a good time to stop and share some of my thoughts on Wrath thus far.

For starters, the environment is much better than BC.  Between the shadow improvements, more detailed terrain, and just generally better zone layouts, Northrend will be much more enjoyable place to level.  I think the quests tend to be more inter-related to create a more cohesive lore path as well.

There are technically 2 more zones than in BC as well, although the PvP zone doesn't really count in terms of leveling.  The "level spread" of the various zones is similar to that found in BC. In terms of leveling, the added PvE zone would be kind of like having another nagrand level zone in BC.  I think they've done a good job of designing the zone/quest hub layout (more quest hubs than BC) in way that will reduce congestion, even if only slightly, from what we saw in places like Hellfire Pennisula.

As for gear, I have now replaced one thing.  I swapped out my [item]Carved Witchdoctor's Stick[/item] last night for the Wand of Blinding Light. All of the other gear I've seen pales in comparison to the T5/6 level gear I've got.  The stats that Blizzard seems to be using to differentiate between healing vs dps caster gear are about what we expected.  Some gear has MP5 or loads of spirit (healing gear), the "dps" gear tends to have either hit rating, or just more crit and haste than the "healing" gear.

So far spec-wise I've tried arcane and frost.  Frost isn't bad, but I think I prefer arcane for leveling.  The amount of damage you can do "on-the-move" with Arcane Barrage(51pt Arcane Talent) is just too good to pass up, especially paired with slow.  Deep Freeze(51pt Frost Talent) ends up being rather situational for leveling, and is pretty much just going to be a pvp talent as expected.  It does hit somewhat harder than ice-lance, so it might work into Fingers of Frost shatter combos in PvE, but it remains to be seen whether or not that damage difference can make it a worthwhile raid talent.  In addition to Arcane Barrage/Slow, the instant Invisibility you can get from the Prismatic Cloak talent and the 2 minute invis cd you can get from the Arcane Flows talent gives arcane a much stronger survivability element than it has now.

I just got Frostfire bolt last night, so I haven't gotten time to really put it through the testing ringer.  I can say this: Shatter combos with the 100% increased frost crit damage AND ignite?  It hurts. Bad. Icy Veins->Nova->Deep Freeze->Frostfire Bolt->Icelance is capable of fairly reliably bursting 11-12k dmg in under 4 seconds, with the target stunned for most of that time and a nasty ignite tick still going afterwards.