Building a shifter is al little more complicated than other classes, but i found it very rewarding.
This guide helped me immensly with getting the underlying mechanics straight, i am however, not entirely sure if the guide applies totally to the final version of NWN:
http://www.gamefaqs....dark/faqs/27914
The most important thing to watch out for is the spellcaster class (i am not even entirely sure if that issue became adressed in the final version, but my guess is a no): Basically the first class you take will be used as caster level for all casting purposes. So if you want, for example, your rakshasa to cast decent ice storms later you do not start out as a monk (1 level *cough* *cough*). Also it essential that you consider your BAB, because if you ruin it early on your shifter will end up weak in offense (especially early on). The third thing you absolutely have to pay attention to is how and what equipment merges on your shapes and this is different and not a constant (and you get no documentation for this in the ingame manual, yay - but the guide above adresses this; btw the creature armor issues, gargoyle for example, have been adressed, to my knowledge). Regarding weapon merge you have to know base damage and to-hit do not merge, but all other properities.
To those claiming the shifter class is overall weak i have to say PVP shifters have been done and done well. The problem is that you really need to know what you are doing and documentation is virtually not existant.
Another thing is to consider that a druid also gets a lot of shapeshifting (wildshapes, construct and dragonshapes for example). And you get decent spellcasting on top of that. So why not simply build a druid when you have to sacrifice so much for a few additional shapes? They even get dragon shape which is basically the crowning jewel of shapeshifting? Well... there are differences, especially in creature abilites and spellcasting.
The breath attack of a druid (for dragonshape), for example, comes at a -4 dc penalty. This doesn't only mean a pure shifter will deal considerably more damage, it also is harder to resist or avoid by save.
The shifter is basically a caster class on its own with acess to spell like abilities via its shapes, as well as a pretty decent melee ability should you feel the need for it.
The wyrmling breath attack is an early strong spell-like ability which can be used on a nearly constant basis, far beyond that what ordinary casters can muster early on. When encountering foes with resistance you can simply switch the color of the wyrmling (and you should as the shapes also introduce vulnerabilities). Its very flexible. You also get true seeing on top of that. I found myself using wyrmling shape a lot. It merges items and armor (though no weapons and remember no stacking bonuses), so it can be considerably beefed up in tougness. Early on its certainly a winner and the breath wepon scales well enough to be of use till you can shift to dragon form. So there you have it: basically your unlimited basic-attack spell form. Did i mention that this is an area attack?
The next notable form is the gargoyle. It merges armor and items plus 34 AC it brings on the table on its own. Furthermore it sports DR 25/+1, so as long as you are not confronted by magic weapons overcoming damage resistance you basically wade through opponents which wipe entire groups at your level range. Its a pretty good tank aviable relatively early, though meleeing through scores of enemies will take time. Epic gargoyle will up that to 44 AC and DR 25/+7. In a low magic environment there is very little that can overome this. Oh and it gets power attack as well as BAB +4. It feels like cheating... because, well it IS cheating in low magic environments.
Then there is the rakasha for casting unlimited ice storms (remember the caster level !!!), basilisk/medusa for flesh to stone, the mindflayer with mindblast, the undead lord (wich actually merges weapons with hefty damage resistances), etc, etc... you get the idea. Oh... and shapes do come with their own BAB bonus (Epic Drider +9, Risen Lord +10, Kobold Commando +13, etc). So if anybody is walking around with +15 weapons thats okay, you are at a slight disadvantage to-hit wise, but if those weapons do not exist... you have a huge advantage at your hands here. You are getting your BAB bonus, no doubt about it. They do not. Plus the extra damage from mergers, of course 
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Now that sounds a lot like min-maxing, but i want to remind you that when buildign a shifter you have to know the mechanics or chances are pretty good you ruin it twoards unplayability. Thats where its bad reputation comes from: poor and missing documentation. What i am saying here is not you shoudl build your shifter twoard maximum DPS, i am just saying don't spoil it. And if you don't spoil it you can play aroudn with it and it will be fun. I don't even include monk levels anymore, because it strikes me as unesthetical. Doesn't have much impact, you don't need monk AC to migrate damage. Not really.
With respect to that i also want to you to take the folloing link to heart when building characters, this approach totally changed everything i looked at charcter building for me. and it works very well:
