This is the game that started real-time strategy. Dune II combined a great license with incredible strategic play and interface breakthroughs that developers are still modeling their systems on today. The game also introduced a branching mission structure into the strategy mix and offered up three separate sides to choose from ( the Harkonnens, the Atreides and the Ordos, each with their own signature units), a feat that wasn't really repeated until Starcraft. Unit design was rich and well-balanced featuring units of raw force, like the Harkonnens Devestator, units of subtle assault, like the Atreides Sonic Tank and units that are just plain devious, like the Ordos Deviator. The game also introduced the random element of the sandworms, overwhelmingly dangerous natural enemies that could swallow an entire assault force before it had a chance to respond. Trent still keeps a boxed copy of this game on his desk to remind him of the greatness the PC games can aspire to.
Other games influenced by Dune 2: Every single one of the RTS titles out there. The Command & Conquer series, the Warcraft series, Starcraft, the Age of Empires series, the Dark Reign series, the Battlezone series and countless others.
And if you are interested: