M 2-55 is a very nice planetary when seen in larger instruments.  Nonetheless it is little known and not often observed or written about.   It is large enough to be obvious at low magnification, making it relatively easy to find.  At high magnification it reveals tantalizing hints of the intricate details that are captured in photographs.  This planetary responds fairly well to the OIII and UHC filters, which are particularly useful at low power.  As with many planetaries the utility of these filters diminishes as you increase magnification. 

At the eyepiece of my 18-inch f/4.5 I noted this one as, "Nice!"  At 97x it was barely visible as a smudge.  The addition of an OIII filter made it stand out well as an obvious PN.  At 270x the view was better, with hints of internal detail.  At this magnification it is quite large in the eyepiece.  The OIII made the background darker and produced a hint of annular structure.  The brighter portion appeared, "sort of square."