ambitious...I will just do four editions
ADD1
Good: Flavor, style, and mixing swords and sorcery just right to start making D&D its own genre. Also, probably just enough options in the core (for the time)
Bad: From OD&D to AD&D lots of little things have been added for balance, making the game more complicated, but balance (or having thief that just doesn't suck) remains elusive.
Ugly: too many incompatible systems, especially for sneaking/surprising, and too many rules that people just thought better to ignore.
ADD2
Good: Droped some of those ignorable rules and tried to open the game up to a wider range of styles.
Bad: THACO: an ackward compramise that actually complicated the game while not making it better. Pretty much 2E mechanics in a nut shell.
Ugly: Stripped out the swords and sorcery style in the core, kicking out demons, devils, and assasins while opening the door to the great big supplement mountain which broke many games, wasted a lot of money, and evetually helped bankrupt TSR.
D&D3
Good: Kept, or restored, many of the details and some of the flavour of AD&D, while making the mechanics far more coherent. Plus it launched the OGL.
Bad: Under its shiney surface lurked much of the wonkiness of the old rules, new complications, and a surprising break down in balance just about as bad as before.
Ugly: 3.5
D&D 4
Good: Made game play the real focus, and did more then ever before to improve how the game worked at the table.
Bad: Went so far as to alienate some potential fans, but still didn't quite get all numbers or balance (or flavor) right
Ugly: Seems to be all about big multi-monster fights and kewl powers (even if its not)