Pros: Simple layout design and compact for when it was built. Heat sinks outside the basic cabinet for the most cooling efficiency.
LED power meters with each segment being +5db along with peak wattage readings.
Variable input level controls mounted on the back (see also Cons).
AC or DC (switchable) input connectors (RCA).
Lighted A-B speaker switches.
240 watts a channel @ 8ohms
Cons: Could of used better speaker connectors.
The input level controls are mounted on the back panel.
Using the top and bottom panel of the unit for part of it's structural support.
They didn't build them for very long.
Using clear bulbs with yellow and green grommets that burn out quickly.
Summary: All in all to me, the Yamaha M-2 is a good amplifier and in my experience can drive most any speaker that is hooked up to it. I currently have one connected a set of Magnepan MG1's on the mains and another one connected to a set of Magnepan MMG's on the surround with no problem at all driving them.
The one con issue that was mentioned that they were not built for very long was not that it wasn't a good amplifier rather Yamaha came out with a new design (M-40 to M-80 series) which was easier to make and they offered different power levels. Even though the M-2 was not around long, it's basic design came from the P series amplifiers that were used by DJ's and recording studio rack systems in the mid 70's. The M-2 was built between 1979-1981.
I think the M-2 has a warm sound not quite like a tube but I have owned one for almost 30 years and have driven many brands and different types of speakers and no matter how good or bad they were they still had that warm sound.
Another con issue about the structural way it is put together is that the heat sinks which are the side panels are attached to the top and bottom panels. This means that there are alot of screws to take off the top panel to get inside to clean or to change a blown fuse which are inside.
Still for the price I rate it pretty high and very dependable even for their age.