I can only repeat what the others said, really well done graphis, audio and especially environment design. I played v00409, so mouse/keyboard controls where totally fine for me. Again, big praise for the game, and if this was done by one person in one month, it's even more impressive.
Now for the parts I didn't like (again, small gripes vs. the overall game):
1) In some places a small ledge is unclimbable/unjumpable. An example is an area to the left of when one enters the big 'open' area (after getting up the tower and finding the first sphere): 
This happened in more places, and not necessarily where it would make sense to prevent the player from leaving the area.
2) I played roughly 1.5h and got 6 spheres. I know I'm not the fastest, but the average playtime of 30 min you gave is IMO not a useful measure how long someone new to the game will need. This is an exploration game, I'll look at things and will traverse an area multiple times to make sure I didn't miss an exit, etc. In other words, at least a basic save features would be appropriate. Maybe save which spheres have been found after a sphere is put into the big 'chandelier'.
Again, a great game, but especially point 2 is IMO something that should be tackled. Because redoing the same parts of the game again and again is not fun!
Best regards, and thanks for the really cool game!