1: Action Masters. Robot Replicas at least had the benefit of being fairly posable, but AMs were just bleurgh.
2: 'Cybertronian/futuristic' alt-modes. I can live with a few exceptions such as G1 Shockwave and Cyclonus, but so many of the toys just look lazy. G1 Blurr? OK, looks kinda cool if not especially 'in disguise'. G1 Quickswitch? Not so much - even allowing for the 'Six-Changer' thing.
3: Gold Plastic. Ooh, shiny! Ooh, breaky!