About 4-5 hrs into the game. The main storyline does seem to be picking up, and is enjoyable so far. The writing is decent, but none of it has really impressed me too much yet. A definite improvement over Morrowind, but that's an understatement anyway. The PC responses are pretty meh, though. Having only one dialogue choice available isn't very inspiring, and just emphasizes how linear the main storyline is. That said, I'm enjoying it. Boromir is such a dream.
I've also joined another faction - the Blades. I haven't progressed in the Dark Brotherhood quests yet.
EDIT: Er, yeah, the instatravel feature is actually a pretty neat one. Normally, I'd be opposed to such, but if there is absolutely story-related during the trip, then by all means please make it optional. This way, I can focus on the story without having to put up with pointless walking. Now, if they had introduced storytelling (a horseback chase, perhaps?) into the trips themselves (and furthered character development in instances where other characters were tagging along with you), that would have of course been better. But, this is better than not having any of that AND not having a choice to skip it.