Let's assume for the sake of convenience that I am talking about any game released for Wii/DS/360/PS3/PC/PSP/iOS/whatever. Released on these systems more than 6 months ago. What do you still really want to get? If possible limit it to games you've played little to none of before.

Off the top of my head:
Wii: that Rabbids game that was platformer, Red Steel 2, Sakura Wars, Punch Out
DS: Order of Ecclesia, 999
360: lots of indie stuff (Super Meat Boy, Comic Jumper come to mind), those games that came out when 360 was trying to be the JRPG console or whatever, Burnout Paradise, Just Cause 2, Asura's Wrath
Ps3: Little Big Planet 1 and 2, Uncharted series, Journey and other...stuff (yeah if I got a Ps3, most of my time would be with old Ps1/2 games tbh)
PC: WHY DON'T I USE STEAM (that sums it up pretty much).
PSP: Puzzle Quest, Corpse Party, Loco Roco 1 and 2, Lumines, War of the Lions

DS: Solatorobo, Mario & Luigi: Partners in Time, Avalon Code, Nostalgia, Pokémon Soulsilver/Heartgold, Radiant Historia, the Legendary Stafy, Metroid Prime Hunters

Wii: Fire Emblem: Radiant Dawn, Zelda: Skyward Sword, Kirby's Return to Dreamland, Tales of Symphonia: Dawn of the new World, the Last Story, Xenoblade, Arc Rise Fantasia, Metroid Prime Trilogy, Metroid: Other M, Fragile Dreams, No More Heroes, No More Heroes 2

360: Portal 2, Lost Odyssey, Soulcalibur V, Tales of Vesperia, Dead or Alive 5 (not 6 months old, I know), Sonic Adventure 2 HD, Limbo, Blue Dragon

PS3: God of War PS2 Collection, God of War PSP Collection, Uncharted series, Ico & Shadow of the Colossus Collection, Journey, InFamous 2, Metal Gear Solid 4, God of War III

I need to play a bunch of my 3ds ambassador games still.
And of course, a ton of Steam games I purchased during various sales. I hate you Steam... <3

Xenoblade. Although that's last gen now, isn't it?

I just named it this way because it was the least confusing thing I could do without spending several paragraphs defining console generations and probably getting it wrong in the process anyway. Let's not even get into that.

Um... how about everything?
The only game I've bought was Kingdom Hearts 3D, and I've barely played that.

Zelda Skyward Sword..

Uncharted 3. Looks good but it's just collecting dust on my shelf.

You can never go wrong with Rhythm Heaven (DS), Limbo (Steam, 360), Bastion (Steam, iPad, 360), Portal 2 (360, PS3, Steam), Super Mario Galaxy 1 & 2 (Wii) and MANY MANY more great games!

Wii: SMG2, fire emblem, NMH2 red steel 2, S&P2, Wii Party, Bit Trip Collection, Other M, Punch Out!! Fragile Dreams
Xbox 360: Mirrors Edge, Eternal Sonata.

Yeah! I'm glad someone created this thread!
Sin and Punishment: Star Successor, Little King's Story, RE5, RE6, RE: Operation Raccoon City, and both Batman Arkham games (Can't wait to play Arkham City on Wii U )
@hoennishome Don't listen to the naysayers, Metroid Other M was a great game!. Maybe not much replay value after you beat it, but it was really fun!

I just remembered to add Eternal Sonata to my 360 list, thanks to @hoennishome mentioning it

Also added Ninja Gaiden Sigma 1&2 to my PS3 list of my own accord.

Way too many games to list. I just got a PS3, so I'm just getting started on catching up on that library. I've also got tons of Wii games that I haven't started playing yet either. Too many games, not enough time

The games in my back log that I'll probably get to first are Ninja Gaiden Sigma Plus and Lumines Electronic Symphony for Vita.

Yeah those are last gen. But I need to play more Monster Hunter Tri

Zelda : Skyward Sword

I agree with a lot of those games, but Operation Racoon City?? I heard it's a REALLY bad game!

Rhythm Heaven and Xenoblade. I still haven't gotten either.

I've got a list of Wii games I still need to play or get next year, then hopefully I'm gonna be as happy with my Wii collection as I'll ever be. I've got Okami, which I haven't played yet, and I still need to get Sonic Colours, Kirby's Epic Yarn, Kirby's Adventure Wii, and I'll invest in Kirby's Dream Collection if it ever comes to Europe (not likely at this stage, but you never know).

As for the DS, I still need to get the third and fourth Professor Layton games (Lost Future and Spectre's Call), Okamiden, and Mario & Luigi: Bowser's Inside Story. There are a few others I'm looking into, like Fire Emblem: Shadow Dragon, but those four are the main ones I still want to get.

Current gen: Paper Mario SS, Crashmo, Harmo Knight, NSMBU, Pikmin 3, New Little Kings Story, Bayonetta 2, Wonderful 101
Last Gen: RE5, RE6, Bayonetta, MGS4, MGSPW, MHP3rd