I just S-Ranked HL2 and plan to do the same for Ep1.
 
Is anyone else playing through these games now that there are achievements?

Sweet, I didn't even know about this! I had a look through the list and saw it had a lot of funny and creative achievements.

Man, I wish they would roll them back into the PC versions, I'm waiting for Black Mesa Source to come out so I can go on a Half Life marathon, been waiting for about a year now... 
 
Edit: Oh, I guess they did

 I see here on GB 4 achievements duplicated with slightly different names. Steam says I've got 33 of 33. GB say 33 of 37. So far, I'm stuck at an A rank as well as the original poster. Do these discrepancies come up often?

It's currently impossible  to S-rank HL2.
I unlocked all 33 Achievements a while ago, but Giant Bomb seems to think there are 37, as it counts some double.
The ones that are double are the only ones with a description in one copy, and they also all have two spelling variations:

 "What cat?" vs "What Cat?"
"Anchor's Aweigh!" vs "Anchors Aweigh!"
"Two Points" vs "2 Points!"
"Radiation Levels Detected" vs "'Radiation Levels Detected'"
 
I see there is a thread about it already:
http://www.giantbomb.com/forums/bug-reporting/33/hl2-achievement-list-is-bugged/420310/

no shit when did they get achievements?  i am so going in again

just got 2 Points, it's kinda hard when ur getting shot at by an angry chopper

HL2 is fixed, so I also got the S-rank for it now.
 
Ribeye, good luck with all the Achievements; that one took me a while too, but moving way back before shooting made it possible.