Atari- Pitfall 2 (that open world!)
NES- Super Mario...or maybe ROB...or maybe Zelda, but really...Metroid. Metroid had the most lasting "wow" feeling. ROB's was the shortest. Super Mario was actually in an arcade cabinet, so I'm not sure it counts. And Zelda is definitely up there with its gold cartridge and expansive world.
Super NES...Super Metroid. There's just no contest here. I loved Super Mario World, but it didn't truly "wow" me. Secret of Mana was probably also a high mark of "wowness" for me, mostly in that I had never heard of it and I was being shown all of these cool action RPGs at the time, including Illusion of Gaia and Secret of Evermore.
PS1/N64...Final Fantasy 7/Mario 64/Zelda: Ocarina of Time...this generation was probably the most "wow" inducing of all time for me. Each of those titles had me grinning ear to ear playing the whole time and just being dumfounded at the potential for videogames.
PS2/Gamecube...Smuggler's Run (crazy open world, go wherever you want)/Metroid Prime...Metroid Prime was stunning in its expansiveness, the incredible graphics, and just the thought that they turned Metroid into a First Person Shooter (adventure) and I was loving it so much. This title single handedly brought me back into the Nintendo fold.
Wii...WiiSports...nothing gets a bigger wow for me than this title probably, and that includes Mario 64, Zelda Ocarina of Time, and Metroid Prime. The motion controlled game just excited me so much about the potential of the Wii that I almost couldn't contain myself. Of course, the waggle lovefest was short lived, but for the first couple months of playing WiiSports I was enthralled.
WiiU...Mario Maker...wow, you can make all these levels?! I thought it was the nail in the coffin for 2D Mario, and as of this writing they haven't made another 2D Mario. Only time will tell. Also, Lego City Undercover and its beautiful use of the Gamepad. I could finally play one of these open world car stealing games without the guilt of GTA.
Switch...Breath of the Wild, and the moment you walk out of the Cave of Resurrection. The "wow" factor doesn't ever fade, either. Here's to hoping its sequel can achieve the same thing.