Very good and interesting game
Good variety of weapons, items, enemies and bosses, and excellent graphics.
Upgrades and Achievements, though of course welcome, were sort of the weak point: the Soul Summoner isn't too useful once you already have a 1000 souls (could've been better if it meant a total of 1000 souls collected including those expended), and the Shadow Dancer achievement seems almost impossible. Maybe on Easy difficulty... And weapon upgrades could maybe have been more interesting than just increasing damage.
Still, a totally enjoyable and challenging game, hopefully indeed To Be Continued :)