IceWM is a window manager with absolutely no pretensions. It is here to manage windows, and it manages them. It gives you a menu and a taskbar. There is a customization interface that's all wrapped up in one program, similar to Window Maker's, only here it's called IcePref. If you expect more, you are looking in the wrong place. IceWM is to window manager what a military-issue MRE is to food. It is adequate and efficient in a very well-thought-out way.
IceWM is another hard-to-find desktop, with maybe a 2% chance of even coming installed in a distro. Upon seeing it, one understands why: not to say that it's bad, just that it's hard to imagine it attracting a wide base of rabid fans. If Xfce is the no-surprises desktop environment, IceWM is the same thing in a window manager. Let's face it, IceWM is boring, perhaps even deliberately so.
It has dozens of themes, which are not much more than color schemes with different shapes of buttons. No matter what you do to it, it still looks like IceWM. However, within this limited space, theme designers have managed to do some interesting things with the looks. Pixmap images are present in some themes, mostly to style the buttons on the taskbar.
It does have excellent performance. Very fast and never has trouble. It politely does its job and gets out of your way. Since this is the stated purpose of the development team on the home site, you may count this as a win. It is also very newbie-friendly. It is simple to a point where if you took more than an hour to learn it, I'd begin to wonder what was wrong with you.
IceWM is dedicated to being no-frills. It takes the philosophy that a window manager should not call attention to itself. IceWM takes this to the point where it's almost invisible. "Shy" might even describe it.
I'd recommend IceWM for the user who just doesn't care very much about desktops in general. Hey, you're here to USE the computer, not sit and gawk at it!