Since Cataclysm has placed such a large focus on new players and the leveling experience, I decided to use some of my beta time to roll a new guy to see the changes. On my live server I'm at the character cap already, and will have to delete a mule just to roll a goblin so I won't get to see much of the new content on live. So, I started up an undead warrrior; undead because I've always liked the Forsaken lore and warrior because I want to tank.
Very early on I'm impressed with the new level of story the quests show; it isn't all 'kill 10 rats' anymore, you're involved with several NPCs for more than single quests. There are also quests that begin automatically when you kill certain mobs (they don't even require drops), quests that complete and chain right in the field, etc. In Deathknell some of the quests are similar (first you kill undead, then hounds/bats, then spiders) but condensed: you don't need 10 of each type of undead anymore, you need 10 total, collect 3 bat wings instead of 8, etc. Generally they left the key story points of Tirisfal Glades intact while tightening it up, adding some new plot threads, and streamlining your path throughout the zone. Example: Once you hit Brill, you're given quests to go up to Garren's Haunt. After completing the quests there, you're sent directly to Agamand Mills without having to return to Brill to pick up new quests.
Once you're done with Tirisfal you head down to Silverpine, where the focus is on the Worgen. You battle the Worgen directly throughout the whole zone, eventually taking the fight into the city of Gilneas itself. This zone was a lot of fun, and felt almost completely different than it's vanilla version. You're working directly for Sylvannas here, and it really immerses you in the war going on between the Forsaken and the Worgen. Once Cata launches I recommend everyone go quest through this zone just to see an example of quests that put the War in Warcraft.