As far a spirit shaman goes, just go minimal WIS (16 is what I usually go), make sure you pick up blood magic (cast extended regenerate before you buff or go into a situation where you absolutely will cast spells every round), use flameblade and fireseeds (though, if you use fireseeds be sure to ward your party as they will get hurt) for sustain. It is pretty much like playing a none-shifting druid. From there on, you use the usual suspects for DC spells.
Spirit Shaman 19/Hierophant 8/Blackguard 3 is fairly strong. You get divine shield, 32+Spell Level DCs (33 if you use echoes, and another +1 to conjuration/evocation spells if you happen to pick up Elven Ceremonial Armor and use Fullplate instead of Mithril Fullplate).
http://nwn2db.com/build/?285797
You also end up with 58 AC with Divine Shield, which can be pushed to 60 with an Improved Mage Armor wand.
Your DC will be slightly higher overall than most druids (shifting or none-shifting, it doesn't matter), and it will 1 lower in respect to a particular school, as most druid builds will have room for Epic Spell Focus. None-shifting druids can typically push their DC higher, but they do lose out on dragon shape and end up with slightly (around 3-5 points, depending on the build) lower AC than a build like this thanks to Divine Shield (they typically have room for ICE to boost their AC up a bit).
Mechanically useful feats include Recall Spirit, Spirit Form, Favored of Spirits, and Spirit Journey. The others, however, are still handy for RP.
Essentially, spirit shaman is a none-shifting druid which, in exchange for a slightly (1-4, depending on how the build goes) lower DC potential and no immunities (to crits, stunning, and the like) gets Recall Spirit (Raise Dead), Spirit Form (2x 5 rounds of displacement), Favored of Spirits (Contingency Heal, very useful with Blood Magic) and Spirit Journey (Ethereal) as well as more flexible spell slots and slightly higher AC (but reliant on Divine Shield).
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That said, spirit shaman specific abilities could use some work.
If I were to change something, I would:
*Give Spirit Form a longer duration (1 round per spirit shaman level) and more uses in the epics (1 at 26, and 1 at 30).
*Give Recall Spirit 2 more uses/day, 1 at 20 and 1 at 28.
*Give Spirit Journey 1 more use/day at level 26.
*Make Spirit Who Walks actually useful. Currently, it is 5 DR/Cold Iron, +3 vs Enchantments, and Low Light Vision. Instead, make it:
10 DR/Cold Iron, Dark Vision, and Immune to Sleep.
Both below could be implemented from PnP:
*Guide Magic at Spirit Shaman 10. Give +1 Concentration/Spirit Shaman Level.
*Give Exorcism at level 13, with a DC equal to 10+Spirit Shaman Level+CHA for half damage, same as Chastise Spirits. Damage would be 1d8/Spirit Shaman Level instead of 1d4 but it only targets a single spirit (or creature being possessed by a spirit when applicable in RP). Make it use 1 use of Chastise Spirits.
Something that could be implemented ourselves:
Sap Essence:
At Spirit Shaman 15, you can expend 2 uses of chastise spirits to instead drain 1 level/5 levels of spirit shaman from a target.
Dominate Spirits (Specific):
At level 22, you can expend 1 use of Chastise Spirits to enslave a particular hostile spirit to your will and dominate it. The DC for this ability is 10+Spirit Shaman Level+CHA.
Dominate Spirits (Environment):
At level 25, you can expend 3 uses of chastise spirits to summon a swarm of various elemental, fey, undead, or animal spirits to your location. You can choose what kind of spirit you desire to summon. For every 6 levels of spirit shaman, you summon 1 spirit of your chosen kind. This counts as a swarm summon. You must have detect spirits on for this to function.
Elemental: Summons various earth, water, fire, and air elementals, each summon having a 25% chance of being each kind respectively.
Fey: Summons pixies (wizards) and dryads (druids), with a 50% chance of each being summoned.
Undead: Summons wraiths, with a 5% chance of each summon being a more powerful dread wraith.
Animal: Summons spirit wolves and bears, with a 50% chance of each being summoned.
Just some ideas to make Spirit Shaman a little more interesting, while still keeping its flavor.