Hackworthy.900: Before I get started I want to know if any builds are particularly impossible in the long run because I'm pretty busy and I've only got about an hour or less a day to play. I really don't wanna get halfway in and find a particular playstyle really wasn't fleshed out.
I can't really spare any specific details on builds; it's been more than a while since i played it -- i'm waiting for the expansion to get back into it. What i can tell you though is that after several character builds that i tried so as to have a better understanding of the character development features, i finally settled with a guy named Vyth, a hacker with a love for guns and shadows. Most points went into Agility / Intelligence / Perception and then Guns / Hacking / Electronics / Stealth. As for Feats, can't remember exactly but all had to do with combat (pistols) etc.
Overall, it was a nice build even though i had to reload frequently during battles to try different tactics; there were times when i felt like i wouldn't be able to finish a battle alive, but eventually i managed and it was quite rewarding, especially when stealth was used and things went by the book. Then, a good friend of mine described his assault rifle merc (or something like that) to me and when i heard about the damage he dealt to his enemies, i understood the vast difference of our builds. Obviously his build was powerful (to the point that it sounded like he exploited the game) and mine wasn't and that explains the frequent reloading i had to do in order to continue.
So, regarding your question, i'm not sure if there are builds that are impossible to finish the game with (it may be possible since there are too many ways to mess up a build if you want to), but surely there are easier & more difficult builds to play with and that obviously can make a player to either spend a great deal of time trying to finish the game, restart with another build or quit the game altogether. I think Vyth fell into the first category. ;)