It's ok, but there is room for improvement.
I like the speed of Flubber, it makes the game challenging. The graphics are basic, but still colourful. It's slightly irritating how you always have to start again when you lose, I think that would be fine as long as you had extra lives. I think there should be more features too because it gets dull quickly. Maybe quicker enemies that can only bounce off the wall but still pose a threat and different items to get, such as increased/decreased size/speed, etc. And each time you start a new level, instead of you pressing start before you can see the level layout, you should be able to click it once it's showing the level so that you can get properly ready. I think you should bring out a new version. Try and make the graphics stand out more too, maybe with some improved effects on the ones you have, which are pretty good by the way. Not bad.