It's okay.
I like the flashy penache it has whenever it swaps dimensions.
It was rather confusing to understand at first that the ships I was buying was the full-fledged ship and it would just swap to the other one once bought, seeing as I had initially thought it were simply upgrades that upgraded my damage. So you can imagine I had wasted opportunity, as well as currency, on worthless things that had even caused me detriment.
The game has goals in mind for the player which is always nice to have, but to what end? I don't see much reason to go for achievements if they unlock nothing. Score never really matters much to me either, but that may just be because I'm a friendless clod. But I can't see how one without friends who sends eachother indie games to compete who can obtain the most score may find satisfaction out of it.
If more were to be added, I would applaud the game for it's arcadey appeal, as arcade games are nice, but it must have substance.