Well, there are many more things in HL2(+episodes) to interact with. So I guess it's much easier to make great episodes that in HL.
He can do great things with moments like, Dog throwing Alyx and Gordon into the citadel, or the first time he sees a fast zombie etc...
The only thing missing in HL2 is the unlogical level design which Ross uses to make some funny dialogues(crate smashing room!).