First game that made you appreciate this generation?

So I suspect most gamers have one game that made them suddenly appreciate what this generation had to offer soon after the Xbox 360 and Playstation 3 were released to the world. The game that made them realise the potential of 'HD gaming' and as always stuck with them as the one game they'll really remember when the dust as settled and we're all playing on our Xbox Next (or whatever) and Playstation 4. Asked this a few people I know and got some interesting answers, most are earlier released games in the consoles life cycle and often pretty average games for the most part. But they had something special when taken into account where we came from in the Xbox and PS2. So what was the first game that made you appreciate this generation and all it had to offer?  
 
For me it was Assassin's Creed, the original. Remember buying that game without much fuss and not expecting a lot, I had heard about the weird animus thing after glancing at it in a news article (it was the big surprise at the time) but didn't think much of it. Little did I know I would be sucked into that world to a worrying degree. I became obsessed with making sure Altair did things as an assassin would and even often restarted parts of the game because I didn't like the way I slight fumbled that kill and such. But it was the world that captivated me. HD gaming (yes I know it is sounds corny) as allowed developers to create some amazing worlds and as much as I've loved the Assassin's Creed games since, there was something about the setting and city detail that I felt went lacking in some of the later games. Don't get me wrong, it had it's problems but it will still be the one game that made me appreciate what this generation had to offer. Especially considering how lacklustre I felt the launch of the Xbox 360 was in terms of games for me... Assassin's Creed relit a fire in me as a gamer and made me appreciate what games could do. 

I would have to go with Oblivion. When I got out of the sewers in that game I was blown away by how big and detailed the world was. Spent well over 100 hours playing that game.

Oblivion. I wasn't too into games at the start of this generation, though I did play regularly on my Xbox and PS2 I never felt obliged to get a new console. That changed one day when my friend got an Xbox 360 and Oblivion, our jaws were on the floor at how pretty it looked and how massive the world was. (We never played PC games).

Oblivion was amazing to play as the first game of the gen for me, I was still happy with my Gamecube but my brother bought a 360 and let me play when I came over, I was so amazed I promptly got my own Xbox360 for it.
 
The real game that made me believe we've reached the next tier in gaming was Mass Effect 1 though, I spend HOURS on the citadel when I first arrived there just talking to npc's.
The game is amazing.

Dead Rising. Just all the things you could do. Going down to the underground and seeing so many zombies at once was mind blowing.

Dead Rising. Dead Rising was awesome. Gears of War and Need for Speed: Most Wanted were among the first games I played, but Dead Rising left the biggest impression. So many fucking zombies.

My first games from the generation were Warhawk and Uncharted and those weren't anything special. Next were Rock Band and GTA IV which I got a week apart from each other. Rock Band's weekly DLC showed that this generation would be full of suport for games after their release. GTA IV showed just how far the tech had come. The lighting system in that game still impresses me.

Saints Row for me. 
 
Then Gears (little did I know), then Assassin's Creed.

Oblivion was incredible.

The first game I played this generation was Folklore (aside from a little oblivion which I was thoroughly unimpressed with). I thought it was a neat little game, but I don't think I really appreciated what this new generation could do until Uncharted.

Metal Gear Solid 4.

Gears of War 1

Even in SD the power of the Unreal Engine 3 was something amazing back then.

I bought a xbox360 for Oblivion.

Dead Rising probably. It's a great game overall but damn the ammount of Zombies in the tunnel towards the true ending was crazy!

Gears of War. Played it at a friends house as he had a 360 and I didn't. I basically said 'I need to have this' and eventually did. Got Oblivion following that which actually didn't sit well with me but the scope of the game was crazy.

ass

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Creed

I'd have to go with Oblivion as well. I got sucked hard into Morrowind, but I played it on a PC that couldn't run it at full speed (though, I played it after all the expansion packs came out on a fairly new computer so it did alright). However, as @laserbolts mentions, coming out of that sewer and seeing the hills roll onward as the music kicks in? Fucking video game magic, ya'll.

I then proceeded to beat all of the faction storylines before even beginning the main quest.

Star Wars: The Force Unleashed 
 
Having the possibility of emulating a Jedi and really affect the gameworld around the avatar was mindblowing for me. Seeing stormtroppers grabbing to the ledges so you wouldn't toss them around was awesome!

Trauma Center: Second Opinion.

Some of the best use of motion control in the early Wii era.

GTA IV and MGS4. Those games launching within a few weeks of each other is what made me buy a PS3.

Ghost Recon, getting out of the helicopter into a big city felt like magic back in those days and though it doesnt hold up now, seeing that for the first time just blew my mind.

Those shiny floors in Perfect Dark Zero.

But in all seriousness, it was probably Oblivion.

Darkness

MGS 4

Oblivion or Gears of War, whichever was release first.

Ratchet and Clank on the PS3, the graphics, frame rates and just the way that game felt just made me smile.

Lost Planet Extreme Condition. It wasn't a perfect game, but I had no interest in the new generation until I first saw the trailer for that. It was the Star Wars 1313 effect really, it didn't have to be unique or interesting, it just looked so incredible from a technical perspective that I had to see it through.

Probably Kameo. It was, and still is, visually stunning. And it was a damn launch game for the 360 back in 2005. Also, it's one of the best platformers this generation.

Coming out of the prison in Oblivion had to be one of those moments for me. Hell even the intro movie with that epic music and the flythrough of the world was great. I also have to say Gears of War just because of how polished it was and how great it looked.

Dead Rising. It was the game that made me get into this generation by buying a 360 back in 2006.
 
Then Assassin's Creed was just amazing besides the average game.

Skate was the reason I bought a Xbox 360, but GRAW was the first game I bought. It completely sold me on games again after taking a break for a few years and got me back into it badly. I now have 50+ xbox 360 games so yeah, GRAW is my answer.

Kameo Elements of Power.

Bioshock first, then i stopped gaming for awhile, then borderlands came along and I've been more than game obsessed since

@Anwar said:

GTA 4, it's the reason I bought a now-gen console.

Same here. Bought a 360 at GTA IV launch just to play it.

Oblivion.

Batman: Arkham Asylum

GTA IV , and the still impressive physics engine Rockstar uses in it's games.

@Hockeymask27 said:

Dead Rising. Just all the things you could do. Going down to the underground and seeing so many zombies at once was mind blowing.

I remember after a year of not much but CoD2 and uprezzed xbox ports it was nice to have Gears of War and Dead Rising at the tail of 2006.

Saints Row: The First, Gears 1 and Halo 3.

Some of the stuff in PGR 3 looked far above and beyond what had been done on Xbox or PS2, but as others have mentioned Oblivion and Gears of War were maybe bigger tipping points.

Edit: Almost forgot about COD 2. That game was also incredible and way above and beyond what could have been done on the previous platforms.

Call of Duty 2. Shit blew my MIND!

I'm gonna have to break this down by system:

360: Dead Rising was the first game I played this generation and felt that I was getting an experience I hadn't had before, chalk that up to the unique gameplay mechanics or the fact that I had some many zombies on my screen. It was mind blowing!. Following that the first Gears of War was the first game that made me appreciate paying for Live, playing co-op with someone randomly that didn't want to grief me probably helped. Plus the game looked stunning on my big screen. Plus, it was the 360 game I liked enough to bring over to my friends' places so they could see it and play it in person.

PS3: MGS4, it was exactly what I wanted from a next gen follow-up to one of my favorite franchises. It was the reason I picked up a PS3 and it was worth it.

Wii: Super Mario Galaxy because it gave me the same feeling I had when I booted up Mario 64 in middle school. And Skyward Sword because it sold me on the WiiMotion+

Gears of War 1, TES: Oblivion and Mass Effect 1 all got me pretty pumped for the current generation.

Peter Jackson's King Kong. I keed, I keed. Oblivion.

PGR f'ing 3

Yeah, can I add PGR 3 as well and while I am here, Condemned Criminal Origins, I bought all 3 on launch day, took Kameo back because I got a free copy when I got my free launch 360 from the Pepsi giveaway, good times, I was so excited about gaming.............. :(

Oblivion.

Dead Rising for me. The attention to detail, the things you could do and the sheer amount of zombies on screen was completely mind-blowing to me. Call of Duty 4 was a big one too. How that game could both look so good and run so smoothly was just amazing.