Valis II, a fun game, but too easy, short and basic. If only they had done a bit more with Valis II (more exploration and less linear level design, or, more challenging hack -n- platforming... like Valis III) then it would have been much more memorable.
I still think Valis II is fun, though.
Valis III, on the other hand, is a huge step towards being a solid game. Valis IV, while very nice, has never captivated me as much as Valis III.
The remake of Valis I ... well, I can't even remember what that plays like now...