Age of Decadence is one of the longest RPG in the making by a small and dedicated team (Iron Tower Studio). I remember reading about him about 9-10 years ago and since them I've waited for it to release. The game is set in a post apocalyptic roman empire like world and features turn based combat and lots of C&C.
When starting the game you receive a warning that this game isn't some fantasy dragon killer simulator. When I first played the demo this year I died on the first quest, because I was stupid and tried to fight someone instead of running away. In this game, with a badly made build you can die easily. The thing that you have to remember though is that this is an Role Playing Game so that if you choose skills/stats related to the selected class (background) the game will be just fine to play. Sure, if you try to be greedy you will get killed if you are not prepared. This means that a change to the way you play this kind of games is required. Like a said above, a bad build is easily made if you don't think about the way a class is played. A merchant maybe should't get into fights and instead should try to talk his way out of problems or solve quests. Sure, you can try to spread into many skills but this may mean you will be unprepared for some future situations, so specialization I think is key. I would say this game is similar to Neo Scavanger on this part. In both games you have to think about what you are going to do. Eating uncleaned water or trying to fight a soldier without having some weapon training could be deadly in both games.
Now that the role playing part is described, I think I should write a bit about story. If you read any of the other reviews, you will know this game is full of C&C (Choice & Consequence). Many of the actions you will take will influence the events that you will received in the future and how you will be treated. Kill a guild trader and you may find that an assassin will be sent after you. Believe the words of a shady looking person and you will find yourself dead in a ditch. The C&C part is probably the reason this game took so long to make, since every background should be viable and also different from the others. What this means is that huge ammounts of text are in this game and it's a lot of (great) reading to be made. I don't think there is any game with so much C&C. The only game that has a smaller amount of C&C is maybe the Witcher series, but not even them don't have as many outcomes and ways to deal with situations. Now that I think a bit, maybe Fallout 2 is a bit similar to it. Both are post apocalyptic games, with turn based combat and many skills that unlock different ways to solve the problems. Similar to Fallout New Vegas there is also a reputation system which opens or closes the way you gain access to some quests.
Like I said in the beginning, the combat is turn based, with different type of attacks available for each weapon. Each weapon class also has different uses and special attacks (eg. you can impale with the spear). If you played Fallout 1 or Fallout 2 is should be very similar. You use action points to move, to make attacks, use items (like poison), etc. Related to fight is also a crafting & alchemy mechanic which can be used to turn the balance on your favor in the harder fights. I think that the fights are well made, with enemies trying different tactics to kill you. What is important also to fighting is avoiding damage, which can be made in two ways: dodge or armor (you can't max both since armor decreases dodge chance).
This is a great game and I recommend it to any serious RPG fan. If you only played this kind of games recently, and didn't try older RPGs, this kind of game may seem harder to play but it really is not. It's a game that doesn't treat you like some brain-dead jellyfish. From my part, this should be the game of the year.
TL; DR
Game is great, lots of C&C with classes that play different and turn based combat. GOTY material, now go and buy a copy!