I have the gog version so presumably it's as patched as (officially) possible. I wrangled my graphics card to stretch 1024x768 as much as possible so that was also fine. The talkative hero was, yes, definitely one of the plus points (shame the in-game font is awful and basically unreadable at any resolution). The storyline, like the rest of the game, seemed a little undercooked in places, but it was fair enough.
Its strong points imho was its immersive storyline, as well as a branching system which was triggered by user interaction with the game's environment. Plus, the hero is very talkative, which was very unusual at the time for a fps.
The game uses a modified Quake 2 engine.
Nowadays, there is a widescreen patch available, as well as a mod which fixes and enhances many things in the game
http://www.moddb.com/games/sin/downloads
http://www.moddb.com/games/sin/mods
Pointing out, the Steam version has some of the graphics dumbed down