I just finished the Episode 1 earlier today, overall I am quite pleased with it. IMO the content was definitely better thought out and executed than in HL2. I think it was quite refreshing to play an FPS where you have a companion traveling with you from the beginning to the very end, and especially because normally such companions are pain in the arse, but Alyx did very well for a non-playable character and wasn't an annoyance. For a episodic content, it wasn't too short either and ended again in a sort of cliffhanger.
There were a few moments which I found to be a bit annoying, but these were short and very few. However, I wondered what were these that looked like dynamite cartridges, I couldn't pick them up because HUD displayed I already had a full stack of them but yet weren't selectable weapons.
Episode 1 was good enough experience that I am definitely going to buy Episode 2 as well.

That and the Episode 2 teaser was interesting.