I love it.
Northrend is wonderful. While it seems small, the new phased zone feature in the game is a way for the map to remain small while the play options are expanded ten-fold. Just when you think you've finished something, another quest comes along and opens up more quests to you.
When I first hit Icecrown, I was concerned when I couldn't find a flight path and an inn at the same location. There was a flight path at The Argent Vanguard, but no inn. The closest inn was in The Storm Peaks, at Frosthold. This bothered me for a bit, but it didn't completely deter me from playing here. It was only after completing several quests that a new town with a flight path and an inn appeared. This was a delightful surprise. Then, as more quests were completed, the lay of the land changed and actually remain changed to this day. No more of this "I thought I killed you yesterday!" or "I collected 12 Kobold candles last week and now they need more?" thing that annoys me. While I enjoy being able to do quests over again, those should be daily quests. Regular quests should remain finished. It does make it more difficult to assist others, though, when you can see something that they can't.
I was also both pleased and disturbed to find that there are two different starting points in Northrend. Such a feature truly spreads out the players, so it's not as crowded as it often is at the beginning of a new expansion pack. However, it makes for an even smaller play area, as once you finish the lower-level zones there, you can either not get much experience by playing in an equally-low place, or go on to a harder zone that awards more experience. If you go on, eventually the low-level zones become gray or green, and you no longer have a reason to explore them. I chose the path of faster advancement, and therefore still have not explored all of the land.
Another wonderful thing in the game is the new Achievement feature. This is a great way to keep the highest-level characters playing for a reason. Various achievements, such as exploring an entire zone, completing certain quest chains, earning so much money, etc are all decent reasons to stick around and play more, without needlessly haunting low-level characters. When I was playing in Outland, I hated the fly-by miners/herbalists who would just land on what I was fighting toward (since I couldn't fly yet), take my gather, then just lift off. With the new achievements, more high-level characters are busy working on whatever achievement they want to accomplish and not getting in my way. Very handy.
The Death Knight is truly a great character to play. It's tough to go back to a lesser character after playing a DK. My level 74 shaman takes longer than my 67 DK to kill a given guy and it's trying on me. I can't imagine what my DK will be like at level 80. I've been taking the group quests that require me to kill elites, and I'm able to do it handily. No need for a potion, a group, or even waiting until the elite is your level. Just take the quest, do it, and get your nice blue reward. I've never been so happy to quest.
At this time, though, one of the problems I have is that my 67 DK isn't high enough level to actually take any quests in Northrend. She can handily kill anything out there, but without any quests, it's silly. So, I'm currently spending time in Blade's Edge Mountains, where it seems that no one else is playing. Totally nice to be alone.
The other problem with my DK is that she started with various skills (fairly decent first aid, got riding for free with completion of a quest, and so on). However, she didn't have any profession skills. So, when I finally made it to Stormwind and became a happy Alliance member, I got her some skills - mining and skinning. I was sad to learn that she starts at level 1 just like everyone else. It would be nice if she started at a reasonable skill level like she did with her first aid and her general level (55). As a new miner/skinner, I have to run her back to low level places and try to get her skill up. This means I'm not getting higher in my leveling, and I feel somewhat bad - both for myself not being able to quest, and for lower characters who I have to steal leather or ore from. It took me about 8 hours to get her skills up to roughly where a level 20 would be. But if I didn't try to get her skills up, I just have to pass by the various leather and ore that I come across. Tough choice.
All in all, I'm enjoying the new expansion pack. It's truly a great advancement in the game, and I am looking forward to more phased zones to appear in future expansions.