Rules Changes
Fixed Skill Checks
Skill checks work differently in Maugeter to the way they work in NWN or D&D. Skill checks are "static", meaning if you have a specific, fixed level in a skill (ranks+stat bonus+modifiers) or higher you pass, and if you have less then you fail. In addition, passing by a large margin may produce a greater effect (this is referred to as a "shift" in conversations).
There are several reasons for this. The first is that the element of randomness which makes skills checks an exciting and interesting thing in a pen and paper game simply does not exist in NWN. There is no tension in clicking on a conversation option and seeing whether you passed or failed. Secondly, the availability of quests or items may depend on the outcome of these skill checks, and introducing a random element is detrimental to the "fairness" of this. It isn't good game design or DM policy to decide whether a player gets something important based on a random outcome. Thirdly, as demonstrated in the Official NWN Campaign, writing dialogue which doesn't allow you to take the same skill check again and again until you pass is tedious, and this system avoids the problem; if you couldn't pass the check the first time you won't be able to pass it on further attempts either.
The difficulties of the checks you have to make will take into account whether or not the character could have had a skill at a certain rank at the level you are at. Checks at level 1 will never require you to have a skill above the maximum possible, and even checks at higher levels will take into account cross-class skill use and the like.
The final thing to say about skills is that they are all used. Spot and Listen are not just for finding rogues, they can (under the right circumstances) be used when trying to see things, and outside closed doors. Don't expect to find much treasure under that pile of bones without a decent Search skill.
The game will generally check to see if you have either no skill, low skill, maximum cross-class skill, or maximum class skill ranks and react appropriately. Of course, you can be even better with the right skill focus and characteristic bonus, and occasionally the game will reward you for your expertise.
All Skills are Class Skills
Quite simply, all skills (except for class-exclusive skills like Use Magic Device) are class skills for all characters. In the luxurious environment of a single-player module, I can happily do this without worrying about balance. If you end up choosing a particular class because you think they're "broken" under this system, shame on you.
I have done this because as a DM I have the ability to, say, allow a Paladin of the Order of Law (who are investigators rather than warriors primarily) to take Spot and Search as class skills, but I can't do that kind of thing in NWN. When all skills are class skills, it's up to the player to decide what skills are most appropriate to their class - maybe they're a Fighter, but from a noble magical family and well-trained in the knowledge of Spellcraft, even though he has no inherent casting ability himself.
Rest Restrictions
Resting in Maugeter is assumed to be a night's rest. You can only do this in a safe, private area. Within the city, look for inns or (occasionally) abandoned houses to rest in. You can buy your own property or rent your own room if you like. Outside of the city, you can rest at organised camping spots.
Whenever you rest, you will be transported to the dream world. You can choose to then wake at dawn or dusk.
Experience Points are only awarded for Quest Completion
You don't get experience points for kills in Maugeter. You get them for completing quests, most of which can be completed either by killing everything in sight, or doing something more subtle.
Summon Creature Spells
Dire animals, they're pretty boring, right? Well, actually they're pretty cool, but once you've played a few spellcasters in NWN you might yearn for something with a little more colour. In Maugeter the Summon Creature spells have been reworked so that you can summon something more interesting.
Wizards and sorcerers summon elementals of various types. Druids and rangers summon animals appropriate to their environment. Clerics summon spirit warriors of the gods.
New Familiars and Animal Companions
This one has its own page.