But I was wondering how easy it would be to run with 5e. I've heard most of the early modules were more or less as easy as swapping monster stats, but I haven't heard anything about 4e. I've only played 4e, never ran it.
Playing 4e should have given you enough familiarity that it's not an issue. If you're comfortable running 5e (or have enough experience running earlier versions like AD&D), you should be accustomed to tailoring adventures to fit your campaign and players & their characters, so the module would just be a starting point...
Outside of mining the adventure like a vulture, any tips on converting a 4e module for 5e? Or is it just so off it's not worth it?
The kinds of combats typical of 4e can be too much for 5e to handle. 5e doesn't do the kind of largish, set-piece encounters that 4e modules tended towards, instead, break them up into smaller bites: more combats, but each less complex and, hopefully, less challenging. They'll go faster, leaving more time to focus on exploration (which 5e has specific mechanics for) and RP.
You probably /can/ just map monster->monster where they exist in both games (unless there's some wild level/power differential with an individual monster, in which case, pick something else more appropriate). 5e bounded accuracy means almost any monster can be on the table - it's numbers of monsters you want to watch out for. Just porting over an encounter with a large number of minions could be problematic, for instance, but solo encounters should be no problem unless the corresponding monster is far in excess of the party level. When porting monsters, try to find Legendary versions to stand in for solos, and 'boss' types or overleveled monster for Elites. Use underleveled monsters for minions, preferably CR less than 1, so they can be one-hit-kills. Be very careful when it comes to outnumbering the party, though. It's OK, for instance, if the set-up allows the party to blow away most of them very early on, by opening with some AE spells or the like. If your party lacks such resources (or even tends to be too stingy with them), avoid outnumbering them by much.
Non-combat, a 4e module might present you with some Skill Challenges. Some of them may map to the 'exploration' system in the DMG. Otherwise, you'll have to break those up into the discrete tasks necessary to complete the challenge, then the players have to tackle those tasks. 5e checks tend to be much lower difficulty than 4e, because of bounded accuracy, so any task that isn't strictly a one-man job can generally be tried by everyone, with it likely someone will succeed. Between those two factors, you can just call for checks from the whole table, instead of going round the table like you would in a skill challenge. Or, if you prefer, you can stick to the 5e core resolution model, and let the players declare actions until they declare and succeed at the right tasks in the right order (or come up with something novel you'd judge would work on the spot).
If the module calls for a group check, just knock the difficulty down a little and use it, because 5e did retain that mechanic. Group checks are ideal for sneaking past a monster or climbing a cliff face or anything else where the whole party has to do it - the idea is strong successes by the majority of the party will allow them to help the few laggards who fail to get through without blowing it for everyone.
Some 4e modules, especially Encounters modules, were very railroady, or at least have certain encounters or challenges that were key to the story. 5e espouses a more open sand box philosophy. While you can always run any game either way, if you want to stick with the classic D&D/5e feel, you should let players use some of the time you save with those smaller/faster combats, to just sort of noodle around, exploring the environment & interacting with NPCs, until they hit upon the more significant elements (or, miss 'em, and some consequence rolls around to affect them as a result).
You didn't mention level, but one thing to keep in mind is that the first level or few of 5e see characters that are actually pretty fragile and limited in what they can take on. If you're used to 4e, you might look at the spell resources of 1st level 5e party and think they could handle a lot, but the durability isn't there yet, and numbers can be overwhelming even with the weakest of monsters, thanks to bounded accuracy. The first few levels in 5e are 'apprentice tier,' and tone of even 1st level 4e modules may be too 'heroic' (1-10th was 'heroic tier' in 4e), for that. 5e characters rapidly grow in hp and spell resources, though, so once you're out of apprentice tier there should be no problem. (Unless you're at the opposite extreme, and trying to convert one of the few Epic tier adventures.)
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