SBCL and Chez Scheme are probably the most advanced dynamic language environments around.
Unfortunately, CL has started to show its age (case insensitive, different namespaces for variables and functions, weirdly named stuff, etc.) and Chez Scheme doesn't have a lot of libraries.
In my experience, Chez Scheme is very small, blazing fast, and VERY high level. It is a great platform to use as a target language for compilers / interpreters. Racket has chosen to go this route, for example.
Can't say that different namespaces are a sign of Lisp showing its age. At least in my mental model, it is convenient to know that a single symbol can name several different things in different namespaces at the same time - e.g. a variable, a function, a type, and a few more that are possibly defined by the user.
Enforcing the "strictly one meaning per symbol" paradigm seems pretty self-defeating to me, since even in a Lisp-1 users can - and eventually will - create their own namespaces, implementing a Lisp-N themselves.
Unfortunately, CL has started to show its age (case insensitive, different namespaces for variables and functions, weirdly named stuff, etc.) and Chez Scheme doesn't have a lot of libraries.
In my experience, Chez Scheme is very small, blazing fast, and VERY high level. It is a great platform to use as a target language for compilers / interpreters. Racket has chosen to go this route, for example.