I am usually always happy with any game I beat. I think it's because of the way I like to play. I try to get the most possible out of games as I can usually.
An example is Morrowind, when I play that I choose to join and beat every guild I can, do every side/road quest I can possibly find, become a vampire and do all I can think of doing for quests and stuff as that, do the quest to get cured of vampirism, continue beating everything else I can until the only thing left is the main quest. Then I go through and beat the main quest as thoroughly as possible... and then I raid every single hide-out, mine, tomb, ruin, and anything else I can find throughout the entire map. Then I move onto one of the expansions... and do the exact same thing. And I enjoy every minute of it. And I don't just flip through the quests either, I take my time with them and try to figure out all of my options and what best suits my character's personality as well as what would be most beneficial to me as a player. For instance, the choice of accepting someone's reward when they are poor and don't have much, or just letting them keep it. The reward may be useful, but letting them keep it may suite my characters personality more, or, if I'm playing a character with that type of attitude (say someone wanted me to escort them somewhere) I may very well just kill them and take what I want.
In NWN I know in some modules it was the same way. My only problem with alot of games, and especially NWN modules... is that I play so thoroughly I often fuck up quests or the main quest or something by doing stuff I'm not supposed to be able to do just because I stumbled upon things I wasn't meant to yet. For instance, this one module I played had a certain area where travelling too far in it would eventually kill you... well shit... that's no challenge for me, I could just drink those sleep in a bottles and get fully rested and trudge through more, and do it again. (scripts on the ground caused you damage) Then there was to be one trigger across the entire area where you instantly die. Somehow I got past that and messed up the whole main quest. After that though I helped the creator by reporting a billion bugs I found... I tend to find bugs really well with that playstyle too.. heh. Usually it ends good as long as my game doesn't get messed up somehow.