But are the Neverwinter nights series any good? Or are just a base of Mask of the betrayer?
Neverwinter Nights 1 has good expansion packs.
The original campaign is crap in that it is long and boring and repetitive. You basically start out in a hub and go on a quest to find 3 or 4 items in 3 or 4 different directions. Repeat 3 times. Not much to it.
Shadows of Undrentide, the first expansion, has a much more varied structure. You go find stuff, play one enemy off the other and then betray them both, rescue a prisoner, end a curse, solve puzzles, and the last boss is a gimmick/puzzle boss.
Hordes of the Underdark, the second expansion, is where NWN1 takes off. It is epic, your choices has consequences, you can fail your missions, and the storyline is convoluted and the backstory has many different storytellers.
Neverwinter Nights 2 has a pretty OK original campaign. It is marred by an overly long first chapter (should have really split it in two) and a very, VERY rushed last chapter due to corporate meddling. The ending has many fans up in arms because it was just lazy, although most of that was attributed to said corporate meddling. It does have quite a bit of plot holes in it, particularly if you play Evil, and it railroads in a way that enrages RPG fans to the core, hence the hate for it.
The first expansion, Mask of the Betrayer, is widely acclaimed to be the best RPG of the lot, and is right up there in the Top 10 or 20, depending on who you talk to. It asks philosophical questions and explores relationships and other pathos. There is a variety of things to do and therefore doesn't seem repetitive or overly long. The characters are, on the whole, fairly well done, although we have the obligatory idiot SJW who never gets a clue no matter how hard even the gods themselves try to pound it into her thick skull. Oh, and she's the ultra high-Wisdom "Cleric". In other words, she is the author self-insert Mary Sue of the game preaching the "though provoking questions", and is the biggest black mark against the expansion.
The second expansion "Storm Over Zehir" is more or less back to Gold Box style of game play: You create a party of 6 or create some and hire the rest from several groups of hirelings (which are mainly crap and don't have banter, so you might as well make all 6 yourself). There is an overland map, random encounters, main quests, side quests, missions, an overarching storyline, and the like. There are some flaws in it, especially with the random encounter rate, which was set far too high, but it is good old fashioned entertainment.
Hope this helps.