Waltorious: Iron Tower Studio were specifically aiming for a game like Fallout and Arcanum when they made Age of Decadence. I haven't played it yet though so I can't comment myself.
Well, I have. It's closer to Fallout 1/2 than to Arcanum, and your ability to explore the world is rather limited - there is no continuous world map, only certain locations (cities, camps, ruins, etc.) are available and you have to know about them to see them on the map. What's more, world map is divided into three regions (which is not obvious when you play for the first time, although you get a prompt if you want to leave the area) and when you leave from one to another
all quests are evaluated, wether you finished them or not, wether you participated in them or not! So, there's much less freedom than in Fallout games, not to mention Arcanum.
Waltorious: it may not give much room for playing a truly nice character
It doesn't. Temporary alliances, business or collective madness, but no friends. You can play as a "diplomatic" character, but be prepared to use those Skill points you should have put into Backstabbing. :> Some quests are solvable in many ways, some only by brute force. And your choice of one of backgrounds for your character at the start of the game is going to influence the first part of the game very much. Joining or betraying available factions is going to open or close large parts of the game, so there are several replays needed, as different characters (backgrounds), to reveal the whole story.