I just played about an hour, here are my first impressions. It's probably worth mentioning that I am a HUGE Bungie fan. However, I wasn't sold by Destiny based on what I had seen.
Turns out it's really good.
As I'm guessing no one wants to read a wall of text (though I doubt anyone cares, haha), here's what I liked and here's what I didn't like.
+Incredible art direction, presentation, UI, and sound design. Bungie nailed it, kudos to the guys in those areas
+Mission structure is great
+Feels like a glorious mixture of Halo and Borderlands
+The world is vast and interesting
+The character customization is a lot deeper and more fun than I thought it would be
+I can dance on command
+The Sparrow controls like a dream and comes in handy
-Gunplay/feedback isn't as strong as I'd like it to be. After coming off of Wolfenstein: TNO last week, Destiny's weapons don't feel as hefty or impactful (though they certainly sound great)
-ADS isn't really needed. I found myself using it very rarely; hip fire worked in almost all cases
-Speaking of guns, maybe it's due to the selection being limited, but none of the weapons I've used so far seem to stand out
-Peter Dinklage's lines are pretty rough
-The bosses take a lot more damage then they should, and draw out fights longer than they should be. I was playing with a couple gaffers and was told it was partially due to our party being different levels, so I dunno