It's got a good type, yes. It's weakness could be worse (...Psychic Weakness. Fighting Weakness. Colorless Weakness. All worse then dark, by far), yes. It's resistance is good, yes.
Psywave actually isn't that bad, just 'cause it's 20 damage per energy, not 10. Just 'cause of that, it's worth a tech slot in some decks, yes. Now, it needs a partner whom is okay and can bide time. Perhaps something fighting type...? Or maybe Electric type... Hm...