First, note that Lisp is actually a family of very different languages, most important being Common Lisp, Scheme and Emacs Lisp, and lots of specialized dialects, like the one Naught Dog used. Also,
Clojure recently appeared, which is a very interesting Lisp running on Java virtual machine. And what they mostly have in common is essential syntax, so it is mostly impossible to generalize.
Of course, one theory about lack of popularity of Lisps is about the syntax. Lisp syntax is very regular, usually minimizing "syntax sugar" to only literals and quoting, which I think scares away people who less read the code and more "look at the pictures", i.e. take cues from graphical appearance of the syntax. To such people Lisp code usually looks like a blob of parentheses, and so they claim that it is unreadable, and hence useless. On the other hand most Lispers, like me, claim that Lisp is supremely readable, because it doesn't distract with punctuation, leaving only the words. Readability is always subjective, but this seems to even more individually varied than usual.
I use Common Lisp, although "use" may be an exaggeration, since I haven't written any program more serious than PNG decoder really, but I think it's definitely better for writing games than Python, as it is both much faster and more more expressive. There are optimizing compilers for Common Lisp, like
SBCL, which are very fast, see for example
http://www.lrde.epita.fr/~didier/resear ... .imecs.pdf. And
macros and
CLOS, which are features very rare among languages.
Of course, there are also problems... the community, which many will claim doesn't even exist, is much smaller and more fractured than of mainstream languages. But it is I think pretty helpful most of the time. Just don't ask
how to create executables 
. One consequence of the smaller community is lesser number of libraries. Most of the primitives for writing games are there (bindings for SDL/OpenGL and so on), but if you want to write a game in CL you must be prepared to sometimes fill some holes yourself.
But I would recommend at least trying to learn Lisp. There is very good
"Practical Common Lisp" book available for free.