Episode 1 was my favorite part of the Half-Life saga so far. Lots of fun stuff in there.
“You did do the calculations… didn’t you Dog?”
Episode 2 had a good story (which suffered from the addition of a new character) and a kick-ass ending, but I hated, hated, hated the last battle sequence. I hate timed battles that depend on me having reflexes that I lost 20 years ago… 
And I won’t say anything more about it to avoid spoilers, but I look forward to being able to discuss the plot later.
You are right about how elegantly everything works in the game; especially how much control you have with just a handful of controls. And it is amazing how much of a story they are able to tell when the main character says nothing throughout the entire game.
Oh, if you have just gotten Orange Box then stop whatever else you are playing immediately and go play Portal. Right now. Really. It’s short, only a few hours, and worth every second of it. You’ll even get cake at the end. 
(You really should play Portal before you play Episode 2. There’s a bit of an easter egg you may miss otherwise. There’s also a Lost easter egg in Episode 2.)