Finished it last night after having put it down for a while. Overall they did a really solid job thus far, but I think HL1 itself just never quite makes the jump from "good" to "great" for me.
I still feel like the platforming is way overdone, and through some combination of it being an FPS and using the Source engine I personally found it difficult oftentimes to really 'tell' where my character was. This was mostly a problem in that
but was a minor annoyance throughout the game when trying to make various jumps.
The final encounter was pretty cool, though I had some FPS issues there. Took me a couple tries, overall I was pleasantly surprised at the difficulty (throughout the game). On that note however, it was really annoying having to disable Auto-aim and "view roll" each and every time I load the game [I think that's source though, I've had problems with source titles remembering settings before IIRC].
Looking forward to the Xen release.