I got it yesterday and took off work. I was 5-6 hours in and it's definitely worth the 20 bucks. This expansion has more story and gameplay than games sold at full retail.
I'm not going to ruin too much with spoilers and what not, but the crossbow and dragon bone weapons are legit. I thought nothing would look better than Daedric or be even stronger than it, but I was wrong.
Being able to smith arrows should have been in the game from the start.
Also when I thought we were done with the realms of oblivion, we're tossed back into it. I give Bethesda their props. It's no shivering isles, but this new realm called Soul Carin fits everything perfectly with the quests and characters.
And that horse that you get to summon? The vampire lord transformation? Man. $20 is a steal for this.