I'm going to run a highly-customized version of B10 - Night's Dark Terror, which is to me the greatest of the classic adventure modules and one of the finest ever printed. Originally made for Expert ruleset, it is a gritty survival and exploration adventure in a huge sandbox format, with quite good encounters and a well thought plot. It is amazing what they managed to fit into 60 pages... I expect to run it for at least 10 sessions, hopefully a few more, although it will require a little work since some of the locations are a bit sketchy.
Having tried 5E for my Dark Sun game past year, I've decided to move back to an older edition. 5e has merits, but its biggest flaw to me is that it is not exciting at all. After polling my players, the generall impression is that they "kind of liked it". And we didn't even reach very high levels, where the problems would have become more acute.
Right now I am torn between two possibilities: AD&D 2e, or 3.5e E6 variant.
AD&D would require little adaptation, but even if I love old D&D I am certainly dubious, since I want skills to play a part during the hex crawl and other situations, and because of the "been there, done that" feeling.
E6 is something I've been wanting to try for some time. I'd complement it with a few houserules for hex crawling and leveling up, and maybe taking some of the good ideas from 5e like Inspiration. For those not knowing what E6 is, it is basically a 3.5e game in which maximum level (Epic) is 6, and from there onwards you can purchase feats with XP. In addition to the regular feats there is specific ones targeted at increasing attributes, BAB, increasing caster level or gaining new slots, or even gaining certain "epic" spells of level 4 or higher (Restoration, Teleport), but which comes as rituals or with rare ingredients. But no HP bloat or inflation, no Dragonball-Z flying PCs that nuke enemies, no buffing madness.
So, Codex, what do I pick? I lean towards E6 right now but I'm still undecided.