I just beat both Portal and HL2: Episode 2 tonight.
I enjoyed the second episode for the most part, I did feel there should have been new weapons added (getting the Magnuson weapon at the very end didn't feel like a "new weapon" to me) But the last fight was very awesome, I agree the ending of the first episode was sorta.......eh?
Hunters are very nasty, especially if you just emptied all your ammo and realized there were gas canisters in full supply in the room next to you....

From a challenge standpoint, I felt the game was lacking. The vorts pretty much do all the work if you aren't chomping at the bit to blow away everything that moves. Some of the puzzles just felt like a re-hashing of HL2 puzzles. I didn't like the cussing in this game either.
Best lines from the Vortigons:
"mmmmm ripe pinatas!"
"I must return to the honorable work under The Magnuson"
That is correct folks, "The Magnuson." Wow, that rules.
I loved the line about the crowbar coming down the hallway, that ruled haha.
There is a ton more but it is late so I'll have to replay it.
I liked the commentaries throughout the game, I eventually stopped clicking on them because they were giving away what was about to happen though, guess I'll catch the rest of them on the flipside. One of Merle Dandridge's (Alyx) quotes was about when the game came out she was curious what people thought so she went on some forum board where someone posted a pic of them with her, and the second post was "WOW, SHE IS UGLY" heh, thought that was funny. Eh, she's actually pretty good looking imho. I find it amusing how some of her lines in the game sound like she's pretty much ready to rape Gordon to death.
Plot: They did a lot more in this one than the first, but I still felt they could have brought out a little more, they're gonna have to let a lot of cats out of the bag in the third one if it is going to be the last of the HL series. I wish there would have been more Gman action in the game, he's just so weird, and he's been in all the games but there's virtually nothing revealed about him, bah. If he doesn't get a lot of airtime in the third I will be a sad panda.
Portal: Absolutely mind-blowingly awesome puzzles to figure out and play through. I peeked into the "advanced versions" of the maps and promptly exited out. I actually had a headache from the first night of playing this game. I do like how they integrated the plotline of this game with HL. I loved the computer's lines, they were really funny but well executed (sarcastic but still mono-tone computer-type voice).
"If you fail, you will receive an unsatisfactory rating, followed by death."
The cake references throughout the game are good too, I'm glad they added humor in HL2: Ep2 and Portal.