Especially on sale it's well worth it. There's nothing groundbreaking here, simply more content for those who enjoy base game. Blue Sun adds three locations with brand new enemies, items, bosses, and optional "contracts" that add extra challenge. Two of these locations are pretty interesting and extensive, comparable in size or bigger than largest ones in base game, like Arisen Dominion or Port Issoudun, with lots of secrets and paths. However, the final one is unfortunately rather disappointing - very lackluster and linear with little to explore compared to previous two. Probably they were rushing to wrap up the DLC. It includes some of the best equipment in a whole game (e.g. improved versions of standard modules, or arguably the best melee weapon). Also worth noting that some enemies grant very high amounts of axions, while being easy to kill, which makes for excellent farming spots.
