Dungeons and Dragons (High Fantasy)- Simple rules on the surface with more complex rules. Most popular RPG, but usually not considered the best. Combat oriented. Heavy reliance on miniatures during combat. Could be run as 3.5 or 4th.
Campaign: This game would focus on exploration or multiple realms. The format would be similar to a “Dungeon a week” formula as players hop from plane to plane.
Campaign: The Worlds Largest Dungeon takes the players from level 1-20 in a single grand adventure set in a single dungeon. 3.5 Only.
Campaign: Return to the Temple of Elemental Evil. A sequel to one of the greatest dungeon crawls of all time, this game involves a manner of investigation and lots of combat to take the players from levels 4-14. Written by Monte Cook. 3.5 Only.
This of course misses a few campaign ideas I have and have had, these are just the easy ones.
So I started with second edition but never really got into it, I played a little in high school but had some games dating back to 1992. In high school third edition came out and Black Iniquity and I played with another of our friends at lunch (and a little during class- oops). Three-Five came out years later and the group we had running at the time converted from third edition. We didn't play too much of fourth edition, and now of course fifth edition has been announced.
The game is fun, lots of options, far too many books. I generally stick with the three core books and a few others.