Having played for decades, I would humbly consider myself a veteran TTRPG GM. Beginning with the Basic Set in the 1980's, I have DMed dozens of multi-adventure campaigns for AD&D 1st, 2nd, 3rd/3.5 editions as well as GMed Mutants and Masterminds, Gamma World, and d20 Modern. In addition, I was a creator and DM for Neverwinter Nights and Neverwinter Nights 2 online persistent gameworlds, running hundreds (literally) of DMed events, sometimes with 2 or 3 DMs and 10+ players. I have been playing 5e since its arrival, creating a custom gameworld to play in as well. Loving the Cypher System even more than DnD, we have switched to this superior game system.
I see “bad” players as those who are self-absorbed, who use out-of-game knowledge, who cheat, or who power game. ‘Great’ players are those who are team-focused, will embrace the role of their characters (flaws and all), and who find creative uses for their abilities.