Giving this game a bad note wasn't easy. If you could buy it for a dollar or two I would probably note it positive but I don't find it worth 15 euro.

First, PC version alone:
No decent tutorial. You need to download instructions to the tabletop Catan or figure it out by trial and error. That's the first frustrating thing at the beginning.
The game can crash. It doesn't happen a lot but it is still possible, so it would be wise to save it as much as you can.
When you want to build a road or a ship at the bottom of the map you might not be able to do it as the map is fixed there and the right bottom menu covers the map.
However, changing view from computer graphics to a tabletop is a pretty nice thing. It can be helpful if you don't have a damn good graphics. There're also some options to choose from and it makes the game more dynamic.

Second, game mechanics:
If you don't like games based primarily on luck, you may not want to buy Catan. It's quite engrossing and needs some allocation of resources but so far I've found the very beginning the most strategic part in Catan. The rest is highly dependable on the dice throws. You may get resources or not. Neither the trade is the best part there. In the worst scenario you end up without resources needed and being robbed all the time by other players while you're trying to save some to build anything. Also, starting first you get more chances to use the best spot on the map. The next turn goes counterclockwise but still the first is the first.
Basic game is quite boring. Nothing much happens there. I found Cities and Knights to be the most interesting map to play. However, it makes the game somehow easier if you manage to get to the dragons in the first turns (you just need to kill a couple of dragons to win the game).

Still, it can be fun but I find it more like a facebook game than a hard strategical/tactical one. Just a nice way to kill some time. So, if you can find the game on sale, you can give it a go. I wouldn't pay for that much though.