I sat down this afternoon to finish playing Portal--I had made it halfway through level 18 previously (with the knowledge, from the first scene, that there were 19 levels total), and today I got through the rest of level 18.
And then got through the first part of level 19, and had to resort to looking for clues online to figure out how to get into the next part of level 19.
(There are no specific spoilers in this entry; trying to keep it vague in case anyone hasn't played but plans to.)
And then spent most of the rest of the evening going through most of the rest of the game.
Finally made it to the closing sequence, but lost the race against time too many times. I did check a bit from another video walkthrough just to make sure I really was on track; sure enough, the next thing I have to do is just a matter of doing what I'm doing faster and with fewer mistakes, to finish before time runs out.
So I set it aside to finish another time. Tomorrow, maybe.
I'm still enjoying it, but I do get a little frustrated with some of the more repetitive parts, and some of the more persnickety timing-and-exact-movement parts.
(There was one bit tonight when I resorted to stacking up assorted objects to stand on in order to get high enough in the air for something. It worked, sorta kinda, but it was slow and frustrating, because you really can't do fine-grained object manipulation in this game; it's like the character is wearing boxing gloves. Anyway, turns out that there's a trick way to get something useful to stand on in that sequence. I'm glad that there are multiple paths to success, but I sure wish I'd figured out the trick instead of spending 15 or 20 minutes on the other approach.)