[Fantomen]

I'd say it's very well worth it if you intend to go multiplayer and/or wants to have access to mods and community support. For me that's absolutely essential and the big WHY in "why I'm playing the game".

If you don't care about these things and only go by the strict difference between vanilla dom2 and vanilla dom3, for the sole purpose of casual single play in elevated solitude. Then actually no, I don't think it's worth the money.