The gravitational effect is absolutely brilliant... just crossing a screen is a fight between player and computer! The graphics are very smooth and well animated, with the only problem being that the same nasties appear on most of the screens.
The concept is brilliant, with stacks of potential for a mega-game, but US Gold's version is far from that. Essentially, it's fun, but I think my general feeling, coming away from it, is one of disappointment.
I usually like shoot-'em-ups, consequently I enjoyed my first few games of Transmuter - this didn't last long though. The more I progressed, and the more add-ons I collected, the more infuriating it became to lose a life and have to restart.