Summary
Pretty good.
The Good
Tubular Worlds is a pretty simple, arcade-type game, so there's not much to say about it. What I will say, is that it's got very good graphics, excellent controls, decent sound and good level design. The variety and "configurability" of weapons makes me happy too.
The Bad
I hate games where you die because of a single shot (R-Type sucked). Also, the game's a bit repetitive, and I wish the music had been better.
The Bottom Line
A decent game, worth playing at the least and buying at the most.