I often hear that Conan D20 (I think by Mongoose?) is one of the best versions of the D20 system. What makes it good?

Very YMMV.

Some thoughts.
First off it is low fantasy. There is no straight up PC caster class. In this it is akin to the older D&D Conan where PC caster classes were few to non-existent.

There are no non-human PC races. Also an element shared with the older D&D Conan.

It has a Terror factor again like D&D Conan which was if I recall right, Horror. It also has factors like Corruption and Reputation.

The classes though are more geared to the setting. Barbarian, Borderer, Noble, Nomad, Pirate, Scholar, Soldier, Temptress, Thief.

Again, like D&D Conan it has Luck points, in d20 Conan's case, Fate points that allow a you to do a few simple things like change certain death to merely 'Left For Dead', turn an attack into a 'Mighty Blow' that does max damage but tends to destroy the weapon used in the process,  Gain a bonus to arry and Dodge for a round, reroll a failed roll, resist one Terror check, Buy off a point of Corruption, and lastly can be used - with agreement of the DM - to alter the world in some small way. The example given was to find some way to escape a jail, such as someone smuggling them a dagger, a guard getting drunk, or a loose stone to break their chains. It has to be plausible in the situation and the character has to work for it. The player only gets three and the only way to get more is by writing down some "Foreshadowing" ideas that the DM can then choose to apply at some point.

Mostly the magic system, which (especially in the second edition and the removal of the goofy generic defensive blast) is really flavorful, actually fairly well balanced and fits the setting really well.

Removing the standard d20 magic system root and branch makes things run a lot faster (still not that fast, it's still d20 after all) and opens up room for some more complication elsewhere such as the armor system and other various combat odds and ends. Also PCs aren't really dependent on their gear much at all (another source of complication removed) and do perfectly fine with the same sort of weapons and armor that random guards are using.

Multiclassing is a bit smoother than in normal 3.5ed and you can make a functional character by simply taking every other level in scholar (knowledge skill monkey and/or caster class) without having to jump through any annoying hoops in order to make a character who won't choke. Power gain is also a bit less steep. These two are a bit intertwined since abilites you get while levelling up don't escalate in power as much so mashing together the first half of two classes works much better, or even doing things like grabbing a random class each level depending on what the PC has been up to still makes for a functional (if not optimized) PC.

And one last thing they lowered the massive damage threshold a lot which means that you have a good shot at downing big monsters if you can get in one big hit which makes combat a bit less of a grind.

Overall solid game but I'd have trouble going back to using fucking skill points again after 5ed. Would like to see a 5edified version of it since I like the casting system a great deal and would love to see that ported over to 5ed along with its other deviations from standard 5ed. The much lower reliance on gear also works well with 5ed.

Quote from: Daztur;1082852Overall solid game but I'd have trouble going back to using fucking skill points again after 5ed.

Funny because I think the lack of control over skill customization is part of what makes 5E completely uninteresting to me.

I played in two D20 Conan campaigns and I'm not a D20 fan. Overall, the game felt very Conan-ish and combat felt bloody and mean, but we were still D&D heroes, whereas I never feel that same D&D hero certainty when I play BRP games. Stormbringer 3rd is my goto BRP sword and sorcery, but every fight risks PC butchery. D20 Conan felt dangerous enough, but still D&D-ish enough to feel powerful like a Conan-ish hero.

While I don't care much for their other 2d20 game lines, Modiphius Entertainment's version of Conan is a lot of fun.

Quote from: Alexander Kalinowski;1082861Funny because I think the lack of control over skill customization is part of what makes 5E completely uninteresting to me.

Then give Conan d20 (2nd edition) a shot. It's still very much 3.5ed at heart with all that entails but the stuff they put in to make it feel more Conan is good solid stuff.

Quote from: Daztur;1082852Mostly the magic system, which (especially in the second edition and the removal of the goofy generic defensive blast) is really flavorful, actually fairly well balanced and fits the setting really well.

That's intriguing. What kills 3.5 for me is high-level magic. Is it Vancian?

Quote from: Aglondir;1082933That's intriguing. What kills 3.5 for me is high-level magic. Is it Vancian?

Nope, MP system (called power points). Which sounds really generic but the implementation is solid. Some bits I liked:
-The "magic attack bonus" stat is used to set spell save DCs and it advances the fastest for the scholar class but it advances with the other classes as well (although they can't do anything with it without the Dabbler feat or some levels in Scholar) so a barbarian 5/scholar 5 can cast spells a bit better than a scholar 5. This makes multiclassing a lot smoother, pretty easy to set up a PC who's a great warrior who dabbles a bit in curses (like Egil Skallagrimson from the Sagas) without borking your character.
-Really flavorful spells, some of them aren't much use in combat (lots of spells that do things like summon plauges to strike fear into a city, not so much fireballs) but give a lot of interesting abilities. One thing I liked was that a lot of spells have a range of "magic link" which requires some kind of supernatural link between the caster and the target like a voodoo doll or something like that.
-Broad range of different schools of magic even though there's no that many spells so depending on what different schools you focus on your caster can feel very very very different from standard S&S dark wizard to wife old woman with herbs and tricks, to kung-fu guy to crazy barbarian berzerker within the same class (with maybe some multiclassing into a more fighty class).
-Base power points are quite low but you can multiply them by doing human sacrifices, strange drugs, dark pacts or by having your acolytes help out and give you some of theirs and whatnot, very in keeping with the setting.
-Some nasty backlash if you fail a concentration check, which is given more teeth than in standard 3.5ed.
-The defensive blast rules are really cool. In second edition each school of magic you learn you get one defensive ability that you can use in emergencies that burns all of you PP. For example one lets your cloak go empty Obi Won style while you teleport elsewhere, lets you automatically pass one saving throw, etc. etc. etc. Makes up for spells having a lot less oomph than in standard D&D and gives casters a good counter to standard "gank the mage!" tactics.
-Very few spells require you to track a bunch of +'s and -'s, funky effects, not much bookkeeping.
-The way the rules are set up you can get an enemy wizard with a lot of power (due to sorcererous lab, lackeys, preparation and stacks of human sacrifices) without the PC class being overpowered at all (the barbarian class is probably the strongest class in Conan d20, surprise surprise), especially since a lot of the powerful spells are things that are a lot more useful to a dark wizard trying to MAKE THE WORLD PAY than an adventuring PC which is nice.