Some thoughts on Medley InterLisp.

In some ways, this project was the fulfillment of me wanting to see what Xerox PARC brought to the table during the peak of Lisp AI research. It was from a time when what "Lisp" was was still being explored. You see heavy traces of the era in InterLisp. 

I will talk on InterLisp only since that is what I wanted to explore.

I did not use "Xerox Common Lisp" nor "Common Lisp" on the machine since I know Common Lisp already.

The Good:
It's Lisp and a fairly fully featured Lisp.
The Inspector.
The Masterscope (track program dependencies through the system among many others things).
Having an editor that understands and balances s-expressions is a great thing.
Documentation - It's built into the system and you can mouse around.
DWIM often catches mistakes and offers corrections then fixes your source.
Just getting graphics on a window is a simple process.
You're saving thousands on getting a piece of history for free. :D
You get 4 dialects of Lisp for free to play with, and their can interop.
Backing up your project in memory is a snap.
A HUGE selection of tools and toys if you can find em. :) (Yes, it has Pacman and Missile Command)
Windows are easy to manipulate.

The Questionable: (Keep in mind I could be wrong here with any item)
Getting mouse coordinates relative to window coordinates.
The window system counts the boarder and title as part of the window region making checking stuff inside VERY annoying.
Arrays start at 1 unless you specify 0.
For loops start at 1 and are inclusive unless you specify.
Position objects seem to have very few math operations.
Accessing record attributes is kind of verbose.
Didn't seem to support closures (if it does, I'm wrong here).
(1 + 1) is legal syntax, infix math may be used via the "Do what I mean" functionality.
Multiplication * (* ... ) is used for comments so you use (TIMES 3 4) instead.