Awesome Music: Just like with AI War Fleet Command, A Valley Without Wind contains a beautiful, melancholic soundtrack by the formidable Pablo Vega. The sequel even contains a vocal theme that, if it doesn't put tears in your eyes, will be close to it, guaranteed.
Demonic Spiders: Sea Worms. They're huge (bigger than some minibosses), move freely through the air, are fairly fast even after your attacks cut their speed, have a huge HP pool with no elemental weaknesses, and are immune to knockback. Their only attack is to touch you, but when they do, it does a non-trivial amount of damage. One of these on unfortunate terrain can wreck your day, a group makes combat even on flat ground just miserable. And this fearsome, Implacable Creature of the sidescrolling world isn't rare, either - in fact they're a common spawn, up to half a dozen or so on any ocean-themed chunk. Good luck.