This is one of my all-time favourite Batman vehicles, and hopefully the official Lego version will be much better than the rather lame Batmobile we got in 2006.
There are a lot of tumbler MOCs out there on the internet, and if you want some tips on how to improve your own, I'd have a look at what other people have come up with. I like different parts of each of the MOCs I've seen. My favourite overall is the one built by BaronSat, but even he doesn't have as many cool side details as yours, like your triple exhausts which I love. He uses two of these pieces for the front windscreens:
(Click on the image for Peeron list of what sets it can be found in)
and he uses these wheels for the front:
But his MOC is larger than yours, so I would maybe try this wheel:
I hope these comments are helpful, and good luck with your building!
Edited by PaulC, 01 January 2008 - 12:23 AM.