When I ran the first two parts of Night's Dark Terror (the river ambush, the raid on the farmstead, exploring/clearing the goblin lairs) it was a conversion: same maps, same in-story motivations, more-or-less the same numbers of NPCs.
Of course I had to assign statblocks to the goblins, had to work out how non-combat action got translated into skill challenges, etc, but that is part of converting any adventure into 4e.
I ran Temple of the
Frog (0e, from Blackmoor) with Essentials rules and fairly direct conversion (monster -> monster, when available, for instance, all the 'encounters' in the numbers and places they were described, &c). It was a very un-even experience for the PCs, because a lot of the encounters were just very quick & utterly trivial (unfamiliar to 4e players), while a few were nasty, but it worked surprisingly well. Just because 4e has a well-worn, dependable guideline for encounters doesn't mean it's not robust enough to handle some old-school craziness.
I wasn't really trying to say that it was "challenging," I guess, to keep the encounters as they were and simply slot in monsters, level for level or whatever standard you choose. That's, essentially, the RPG equivalent of a word-for-word translation of a text, which is (theoretically) always achievable with a bit of circumlocution.
Rather, I meant that if you want a less "uneven" experience, if you want to avoid things 4e does poorly and create opportunities for it to showcase all the things it does well, it seems like all you can reliably keep is the story, a handful of character ideas, (maybe) the monster types used, and the general organization of the maps.
If that's what you want--a well-built, 4e-focused experience--you probably can't port the encounters, because that makes for lots of filler fights, which aren't all that fun in 4e (or at least they have a poor time investment:fun return ratio). On that front, we seem like we agree more than we disagree. To be fair though, I may just be projecting a little, as I did not especially enjoy the "most fights are curb stomps, but you never know if you're giving or receiving until it happens" nature of the handful of B/X (technically LL) sessions I played. (The sessions overall were fun though, very glad I was allowed to play.)
Similarly, if the "most of the maps are way too small" and "not enough maps featured terrain stuff" statements hold true, keeping the maps send like another way to lose out on what makes 4e shine. You can totally DO it, the maps aren't going to catch fire or something (though I'm sure this fact would disappoint many diehard traditionalist gamers!) But it won't work as well as it could.
Circling back to my earlier translation metaphor, I guess what I'm saying is, 4e, at a mechanical level, is a sufficiently different language that you can't just do word-for-word translation. You lose a lot, and don't gain a lot in return. Like translating the Bible to English: Greek, Aramaic, and Hebrew grammar and syntax are...just realized very differently than English. Or for a different, less religious example, comparing/translating traditional Japanese poetry to English. Often, it can't be done while preserving both the form (granting syllables instead of morae)
and the literal meaning of the words, because English words tend to be longer--and we'll be missing all sorts of little bits and bobs like articles. Instead, you have to either abandon the form, or abandon the word-for-word and try to achieve (poetic) meaning-for-meaning. It's similar for Chinese poetry as well (since those languages are fairly closely related), such as Li Po/Li Bai's poem (made well-known by SMAC):
"The birds have vanished in the sky,
and now the last cloud drains away.
We sit together, the mountain and I
until only the mountain remains."
Many of these words would not be present in the original Chinese (a quick Google search didn't turn up the original Chinese text, unfortunately). Articles and sometimes even pronouns, as in Latin, are left to context. But to capture a similar understanding in an English reader as in a Chinese reader, one would need to include them--and alter the structure of the poem to match.
Is that quite the same as what I said? Is this "an English poem inspired by a Chinese poem," or is it the same thing just "poetically translated"? Does the question even have a distinct answer? I dunno.
Perhaps it would just be best to amend my original statement: It sounds like 4e groups will get the best experience from their game by playing "4e adventures inspired by 1e adventures," in the long run, rather than trying to keep as much of the original 1e adventure as is mechanically possible.
