I really don't mind either way, but ESF should just stay on HL, and not convert to HL2 when it is released. (trust me, it's going to be later than September, mostly ALL games are held back a little)
I think unfortunately, many people who use other engines for games, like Unreal Tournament, and Quake for example, only use those engines because they look good graphically.
Of course, looking good is nice for something to have, but IMO I have always thought Half-Life just had a certain flair and fun originality that no other engines I have played on have.
Call me old-fashioned, but I say just because a new engine that rolls along can support more polygons, bigger maps, better models, etc, a game should not be totally destroyed and resurrected for that engine.
Thats my two cents.