The descriptions aren't all that clear. What is the major difference?

Explorer mode: "regular AI will not use crowd control skills (bosses may use them)"

Check out this EE summary thread if you haven't already:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=572102#Post572102

Also, from the D:OS EE Wiki:

Explorer Mode
- The player gets +80% HP & +30% boost to Chances to Hit.
- NPCs get -50% HP & -25% penalty to Chances to Hit.
- Regular creatures don't have any crowd control spells (Charm, Mute, Freeze, Petrify etc.): only bosses have them.

Classic Mode
- The player gets +15% HP.
- Creatures have all of their regular spells.

Raze, can you give us the stats on Tactician?

The wiki lists the other difficulty modes, as well:

Tactician Mode
- NPCs get +20% HP.
- Currently known as Hardcore Mode, this mode gives most creatures in the game additional skills & abilities, including bosses.
[there are also changes to the world, such as an extra explosive barrel in the orc fight at the start of the game, which the orcs can use against the players, if they aren't paying attention]

Honor Mode
- NPCs get +20% HP.
- The user has only 1 save slot, so every time they save / quicksave / autosave, the savegame is overwritten. If a character dies (PC, companion, henchman) the game autosaves.

Thanks. Tactician mode so far has a very good feel to it.

Can difficulty be changed in a running game?

Tactician mode is awesome. I'm enjoying it.

I heard that technician is super difficult, is it?

If you know what you doing, no
But Honor Mode with only one Saveslot.... uh

My wife downright refused honor mode, it sounds so tasty

What does that even mean, only one save slot? Like, you can save as much as you want but you only get that one save slot so if you save at a bad time it's perma gg?

[quote=Zachb34]What does that even mean, only one save slot? Like, you can save as much as you want but you only get that one save slot so if you save at a bad time it's perma gg? [/quote]
Pretty much.The game also autosaves over that save slot if one of your party member dies, so no reloading when a fight is going badly.You have to restart the entire game if your party gets wiped, which wouldn't be so bad if the game was all combat but which so much dialogue and story it seems like that would get tedious.There's still Tactician though if you're just looking for something more challenging than Classical.

I'm just glad they balanced it out for everyone, as mandating perma-death/assembly line gameplay is why I unfortunately don't buy a lot of newer indie titles these days..

Couldn't you just manually back up your save file every once and a while to get around the perma-death?

Probably...

But I believe that the idea behind that game mode is that it is for people who want a further challenge beyond Tactician. If you're just going to cheat and go around the system, then why not just play on Tactician in the first place?