Good concept, look forward to a sequel
I'm a sucker for this kind of "2-and-a-half-D" style - I got thrown out of a shop years ago for hogging Bug on the Sega Saturn - and this game not only uses the 3D concept well, but introduces it in a way that really was both a logical progression and a surprise. I had no idea at first about the secret life at the start of level 5... :)
Like most other people, I feel that in-level checkpoints would have been welcome.
The graphics are very clear and well done, and the music reminds me of that used in the original radio and TV versions of Hitch-Hiker's Guide to the Galaxy, very nice.
Why only six stars? Simply put, I became frustrated attempting to side-jump AND rotate my view at the same time on level 7 without dying - that requires pressing THREE keys at once (eh, maybe I'm just uncoordinated.) Maybe a more "secure" environment to learn this new skill, and maybe a sign alerting you of this new learning experience, would have helped.
Also, the levels seem somewhat static; but I don't know if there are moving platforms or doors or anything like that in later levels.
If there is a sequel, I hope the humour stays intact, and that checkpoints are included. And maybe more interesting/dynamic level designs, even something as simple as texturing the blocks.
And as for "gravity in space"... maybe next time Jason could be exploring in the atmosphere of a gas giant?