Excellent: a combination of C's syntax and extensibility with Common Lisp's speed. That's what I've been waiting for!
And actually, SBCL is nearly as fast as C in many cases. So there's really no reason to not use CL, unless of course you don't like CL.
Every Lisp dialect has some high-level syntax, e.g. quote, CL reader macros, and Arc ssyntax. These obscure the relationship between code and the underlying AST, but the designers felt that the gain in readability was worth it.
How much syntax should there be? A hard question, but I think it would be good for Lisp to move in the "more" direction. Readability is one of the big problems I have with Lisp, and macros, while certainly useful, make up only a small fraction of my code.
But yes, I can't for the life of me understand why someone would want to use TwinLisp.