I too prefer the 1E version and as systems go prefer D&D for Nehwon campaigns.
The MRQ-version is an interesting different approach but is IMHO too light on detail/maps and the wrong game system (I don't recall that many dismemberments in the Swords series - LOL!).
It would have been interesting to see what a version using something akin to the d20 Conan rules would have produced . . . but even then there would need to be more information than in the current supplement.
[While A Guide to Nehwon may have more information on the world it's unlikely to have any more details on Lankhmar. I also feel that Mongoose should have combined both books to remove the duplication but that's another topic . . .]
Actually, the 2nd ed. version had about 7-8 adventures for it. Unfortunately, many of those were created by Dale 'Slade' Henson and had little to no relationship to established characters and places. I remember in particular an adventure in a softcover collection (Wonders of Nehwon?) where Quarmall was depicted as a small wooden fort!
I remember the 1e stuff being a little darker atmosphered than the 2e. I have a lot (though not all) of the 1e and 2e Lankhmar stuff. I haven't seen the Runequest one.