A character class in 3rd Edition D&D.
The Spirit Shaman is a variant form of the Shaman class from the splatbook "Complete Divine", one that has been made more "mainstream", since it's predecessor was first printed in Oriental Adventures and consisted mostly of a combination of elements of the Cleric and Druid classes.
The writers decided to go for a different avenue with the Spirit Shaman instead and make it completely unrecognisable from the previous version.
This one has much more of an rugged, outdoors-y feel to it. It has better fortitude saves, more spells per level and LOADS more supernatural abilities, though all designed to deal with "Spirits" (defined as Incorporeal Undead, Fey, Elementals and anything Astrally projecting) but impressively, they gain a spell like ability that can be used to Raise Dead with no penalty to the target. Eventually Spirit Shamans end up transcending the mortal world and become Fey. In fact at first level, they assign themselves a Spirit Guide which later gives them the ability to do various things, such as Detect Spirits for them (unlike the regular Shaman's ability to just "see" spirits), allow them to resist enchantments and eventually can do the concentration on spells for them if they are too lazy to do it themselves.
One unusual thing about the class is that while they are officially spontaneous casters for qualifications, they "retrieve" their spells known at the start of the day letting them change their spells up. This helps them cure conditions between adventures better. This would become the standard system for casting in 5th edition.
Playing a Spirit Shaman
Is the class worth it? It depends, while it does have more spells per day the class actually casts spontaneously like a Sorcerer does and in fact only knows a tiny amount of spells from the Druid list (only 3 per spell level in fact). Though the Shaman is allowed to change the selection each day by communing with their Spirit Guide, which in theory gives them day to day versatility like a prepared caster.
Ultimately, the class’s tier depends largely on how strong you view the Druid’s spelllist as being. Druid has always been considered the weakest of the core full casters in terms of raw casting since most of its unique spells only work against a certain creature type (animal) that’s rare at higher levels, depend on certain parts of terrain (natural plants tend to be quite rare deep in a dungeon), or buff the animal companion a Spirit Shaman doesn’t have. While Druid has some standouts and things that are otherwise split between the Wizard and Cleric, they tend to come at a higher level than either and get their Tier 1 stats from the class features they have combined with their casting than just the casting on its own. On the plus side, Druids are core full casters and get new spells in almost every 3E book while the Spirit Shaman knows all of them. This means opinions tend to skew based on how much splat is dug through for shiny Druid spells or ways to expand the class list. Since the tier system was designed to base a class primarily on core and the book it came in instead of whatever the munchkin dragged in (with the occasional second placement if a single thing greatly impacts the class’s performance), this means the Spirit Shaman tends to get placed down in Tier 2 or even Tier 3 (but mostly 2).
As for a dip level for those that just want some minor spellcasting powers without interrupting their primary class progression much, a single level or two of Spirit Shaman does not you any amount of low level freedom that a different class could not already give you either. It really depends upon your attitude to the Spirit world in your campaign then. But if you're in it for the class features, then you're better served remaining in this class to it's completion, since the class features are it's strong suit.