Which OSR adventures are most useful?

The things that have been most useful to me, running D&D:

Dyson's Delve I & II - for my swords & sorcery Wilderlands campaign. Tons of great dungeons, and then tons of beautiful unkeyed maps to make your own.

Most of the adventures from Basicfantasy.org - Adventure Anthology 1, The Glain Campaign, and Monkey Isle in particular are all great. Saga of the Giants looks cool too. They are in the style of Moldvay-Cook/Marsh Basic/Classic D&D adventures, the printed versions are sold at-cost from amazon. Most very good, and unbelievably good value. I use them for a Mentzer Classic D&D campaign set in Karameikos.

I also enjoyed Venger Satanis' Liberation of the Demon Slayer (for the Wilderlands game), tons of inventiveness but it's a bit of a mess, the maps need re-keying.

I think the key for me is that OSR adventures need to be modules I can plug in to my own campaign. I recently bought Stonehell & Dwimmermount - these are well done megadungeons, Dwimmermount especially is fantastically well presented, but they are designed as tentpoles for your campaign, not plug-in elements.

If you wanted to kick off a megadungeon-focused OSR campaign in OD&D style, then I'd recommend Dwimmermount. If you are doing your own wilderness sandbox dotted with dungeons in the Judges Guild mode then the Dyson's Delves (you can plug them in to eg Rob Conley's Blackmarsh or Points of Light). If you are doing episodic 'dungeon of the week' - the default Moldvay & Mentzer Classic D&D approach - then the BasicFantasy.org stuff is best, though much can also be used for sandboxing.

My 4e D&D Task Difficulty System

I think the 4e DMG pg 42 table should have explicitly stated baseline assumptions for "This is what a Low Heroic environment looks like", "This is what a High Paragon environment looks like" etc, to make the DCs & damage feel grounded in the world rather than free-floating. The GM could always move the slider if he wanted a Low Heroic game set in the Elemental Chaos. There is a little bit of this in the general Tier descriptions but it's not tied in to page 42.

Running high level 4e, I've also had a problem with "all monster abilities scale" vs the fixed DCs, rather than with arbitrarily ascending DCs. You get eg high level minion monsters that can climb walls like ninjas because their level & STR makes them great at Athletics, so they can swarm up regular DC 20 walls no problem. I can see why some GMs just have *everything's* DC scale by PC level, which is functionally equivalent to nothing scaling.

What I did with 4e was to create my own DC table based on the environment rather than on PC level, as so:

Task Difficulty
Easy Heroic: 10
Medium Heroic: 15
Hard Heroic/Easy Paragon: 20
Medium Paragon: 25
Hard Paragon/Easy Epic: 30
Medium Epic: 35
Hard Epic: 40

So eg navigating the slippery ice field might be a Hard Heroic/Easy Paragon sort of feat, that makes it Acrobatics DC 20.

With the usual +/- 2 for circumstances (so a particularly hard Epic task is DC 42 - unpicking the lock to Orcus' vault, say) that then covers every possibility in the official task DC table, which runs from 8 to 42, and I can keep it in my head and assign appropriate DCs on the fly without caring that eg my PCs are currently level 26.

My old-school D&D stat gen method

I find 'roll & assign as desired', the default in 1e AD&D, a very bad way to create PCs, it's basically 'variable point buy'. Default Array & Point Buy work best for the 3e/4e/5e attribute mods systems. But for old school D&D I now use an 'assign when rolled, default to in order' system where each number rolled is then locked in to a particular stat (eg the first roll either goes to STR or is assigned to a different stat, then 2nd roll goes to INT or one of the other 4 remaining open stats).  So the final attribute rolled is always random - this is often CHA, since it's at the end of the STR INT WIS CON DEX CHA line.