I have some initial observations about multiclassing in Pathfinder.
The big changes:
Favored Class Change: this is really not terribly significant as it was in 3.x. On the one hand, it allows freer multiclassing and prevents railroading races into particular classes, but the benefit of actually having a favored class is fairly minimal. Arguably, the favored class rule simply favors non-half-elf single-classed characters, who get to use the extra skill rank or hit point every level.
Capstone Abilities and No Dead Levels: these two game elements were obviously put in place to reward single-class characters for sticking with a class, and to address the multi-class bloat that occured in 3.x. The downside is that there is now a heavy price to pay when multiclassing -- the opportunity cost of never being able to get the higher level abilities. This is huge for all classes.
Class Skill Revision: Allowing class skills to apply to all future levels is a big change. This favors multiclassing; once you have Use Magic Device as a class skill, for instance, you can keep adding ranks to it even if your future levels are in classes without that class skill.
Comments:
In 3.x, there were essentially three kinds of multiclassers. The non-spellcaster who wanted a piece of every non-spellcasting class for optimization purposes, those who multiclassed to qualify for a specific prestige class, and those individuals who multiclassed purely for character concept.
After trying several different character builds, I am of the opinion that you had better have a very good reason to multiclass: either you are aiming for a prestige class or have a RP/concept reason to multiclass. Let me show you why.
An example of multiclassing that is worth it
Let's say I make a half-elf who wants to be a Cleric/Wizard Mystic Theurge. I'm putting most of my character points into Int, Wis, and maybe some Cha if I can spare it. If I take 3 levels each in Cleric and Wizard and 4 into Mystic Theurge, at 10th level I am a 7th level caster in each class. Let us assume that my DM lets me take the Practiced Spellcaster feat (from 3.5) two times and raise that to 10th caster level in each class.
What have I given up by multiclassing? The big ones are wizard bonus feats, lack of progression in arcane school abilities, divine channeling effectiveness, and lack of progression in domain powers. Also, I don't have access to 5th level spells.
To me, this is a fair exchange. I'm getting a huge amount of versatility but am only about 2/3 as powerful as a single class 10th level cleric or wizard. Probably the biggest downside to this build is the pitiful divine channeling effectiveness. Then again, Mystic Theurge has its own capstone abilities that will hopefully make the trip worthwhile.
An example of multiclassing that is not worth it
One of the more common builds in 3.x featured "splashing" of class levels to get cool class abilities (and some high saving throws) for non-spellcasters. Common splashes were Barbarian 1 (for rage and fast movement), Fighter 4 (for three feats and weapon specialization), Ranger 2 (for combat style), and Rogue 2 (for sneak attack and evasion).
So let's build a level 10 3.5 splasher in Pathfinder. We'll go Bbn2/Ftr4/Rgr2/Rog2.
On the plus side, we do get a lot of fun class powers and have a BAB of +9, a great Fort save and good Ref save.
What exactly are we giving up here? Well, the favored class rule is going to cost us at least 6 skill ranks or 6 hit points. And then there's the higher level class powers we will NEVER get, like:
* Greater Rage, Damage Reduction, Rage Powers ...
* Weapon and Armor Training/Mastery, more bonus feats ...
* Ranger spells, favored enemy progression, animal companion, favored terrain ...
* Rogue talents, more sneak attack ...
So while the splasher is fun in the early-mid levels, by the mid-late levels he flames out in comparison. The splasher will maintain a good BAB and saves but will fall behind due to the lack of progression in core class abilities -- unless of course the splasher's intention is to swap into a prestige class that has its own capstone abilities that justify all the multiclassing.
