should I buy it?

[Edi]

Sombre said:
The dom3 modding scene also trounces the dom2 one royally, if you have any interest in mods/modding.

Yes, modding capabilities have been drastically expanded.

Besides that, the difference in the modding scene is in large part a function of better documentation being available far earlier than was the case with Dom2, which has led to more mods being made. When you look at the Dom2 scene, the number of mods practically exploded after the Dom2DB came out because otherwise it would have been a pain in the arse to get that info.

Compared to release date of the game, the Dom3 DB came out long, long before Dom2 DB did and it is better organized than its predecessor too. It's also going to get more user friendly after the next patch.