From Dailybits: “Overall, though, Leviathan is a considerable improvement and holds a lot more promise than the earlier Europa Universalis expansions. The favour and development systems make peaceful, diplomatic gameplay more viable and introduce entirely new ways to play the game. It’s well worth the investment if you play a lot of Europa Universalis, and a good excuse to pick up Paradox’s new subscription service, which gives you access to all expansions for their games.”
Source: N4G PC Europa Universalis IV: Leviathan Review – DailyBits