The most addicting game I ever played was Pokémon Gold. It went like this...  Pick Cyndaquil, evolve before sprout tower, catch Pokémon only as HM slaves, beat the E4 with my lv. 100 Typhlosion with Earthquake and Thunder punch to kill any type advantages against me. Game over, do it again in three hours. I tried to see how fast I could beat it.  Just couldn't stop playing!

In my addiction, I think of tetris, Mario and mega man

Can't believe no one has said WoW, it just has so much depth and so many expansions and different content. I have quit several times for my health but its just a fun game it's not as hard as many other MMORPG, it's beautiful and has your moneys worth in game play. People have literally put in years of played time on the game and it has 33 million players and just keeps growing. I personally love it just don't have time to play it with a son and such but in my opinion it is the most addictive game I can think of...people have died due to WoW that's gotta count for something on the addiction level 

I'd have to say all the halo games because I love the story and vehicles in it. I could play for hours and not get bored. 

   Wasn't my favorite game but as for addictiveness I'd say Smackdown Bring the Pain. I was hooked for too long on that game.

the most adicting game that i have ever played was ratchet and clank

I'm going to have to say Ocarina of Time. I got that game bundled with my 3DS and played nonstop. It's such an excellent game. Runners up are probably any Pokemon rpg, the Megaman Battle Network games, and the Deus Ex games. @Sephirothxxxxxxxxxxx I agree with a lot of your games you mentioned.

Super smash bros brawl is the most addicting I even still play it 

Most Addicting?
Probably "Enter the Matrix the Path of Neo."
We saw the Flix and still played the game. All the way through. Watched the cut-scenes Again (all movie clips). Couldn't get enough.
Though I should say "lock on" feature games.
Syphon Filter 1 and 2, Bushido Blade 1 and 2, Devil May Cry 3 and 4, Zelda O.O.T. All have a similar feature. It could be the fact that the action goes as planned but the camera goes wild. And it gets to be fun just seeing what the camera does. In a manner the game can be played the same way but never looks the same.

Saints Row 2 was very addicting. As Was Mercenaries 2 and Crackdown 2. Dead to Rights.
I could go all day with this one but I just love how games have evolved. I dig playing with the camera and seeing the action differently.
In Zelda O.O.T. with the Tower Gannon Fight there's a moment where Link can fall and if you tap the hook-shot button the camera delays for a split second to almost gives the impression that Link is going to do an Impression of "Bat-Man". (He doesn't.) I Love those moments. You get into the action and it feels great just seeing a fun stunt being pulled.
In Syphon Filter there's a level where you have to escape a base on full alert. if you go through with the shot-gun or Machine-gun its hard. But if you Switch to your Pistol and doge every few seconds the camera and characters play around and it looks like Gabe acts like a Ninja avoiding gunfire and capping a few foes. (Like a John Woo Movie).
Hundreds of moments like this are what I crave.

I just Love playing around with the camera in games.
Some of the music videos on you-tube have been amazing because of this one invention.
I now listen to music that should only appeal to younger people.
Thank You "Lock On Feature".
Good Luck To All.
I'm Done. Stick a Fork in Me.
Peace.

The most addicting game I played was Mario Kart 64, it was a really game.

Pokémon,stick arena plant vs zombies, but my favorites are mega man 3, grand theft auto sa, dbz, and super smash bros brawl.

Of all time? Probably Gauntlet. Don't know why, but we played that game for hours. Epic three-day marathons were not unusual, with time out for naps and food and the bathroom (but not showers. Mom was always thrilled...) 

But I might have found a more addictive and terrible game-*glares at Harvest Moon game* Why do I play you so much? Whhhhyyyyy?

Hmm, it is actually very easy for me to get addicted to almost any game I find interesting. Arguably, I would say my Dragon Quest series was the most addictive set of games since I continue to replay them. However, I am also a die-hard Dragon Quest fan-boy.

I suppose online games is where I get most addicted. Really got bad when I played Ragnarok Online. Called out of work a few times so I could play, canceled on family plans (where I could)... One time, my family made me go on vacation and I was so stressed out about a war game in Ragnarok Online, I had to have my friend (who also played) call me to tell me how things went and such (which, being equally obsessed as I, was eager to comply with explicit details).

Breaking from that, I also went hard into Maple Story. It got really bad where I would let the game cut into my college classes. My best friend, showing her very supportive prowess here, would even help me level up characters I had on a second account, and when that service was not needed, get me snacks when I was doing some hardcore doubled experience grinding.

NEStalgia (an "indie" game on a site called "BYOND") was another vice I played with my neighbor a lot. We were both unemployed, so we would spend so much time with a friend we made on there who hailed from England trying to perfect so many of our characters and getting through stories... not to mention taking vengeance on those who disturbed us (PvP server). Interest waned between us all though, and although I still check to see if it gets updates, I have essentially stopped playing.

To a much lesser extent, Neopets was very addictive while I was unemployed; I played the luck-based games so much, I started getting high scores! I even won a free Neo-Cash card! Sadly, once my account got stolen, all desire to go back to it was lost. I just really enjoyed the luck based games that made me feel I was in a casino; let me get some gambler lust out.

Today, my video game addictions lie in whatever I currently want to beat. Right now, the addiction is in Pokémon Conquest.

EDIT: WHOOPS! I forgot, Animal Crossing for the DS and Wii was rather addictive! Essentially was like doing your chores playing that game to get a great town and friends with all neighbors! The wii version pales in comparison to the DS version though; it is much easier to maintain a town on the go then having to sit down in front of your TV, load up the game and play. (I do eagerly await the 3DS version though!)

Castlevania games, Specifically SOTN and afterwards, once they added the rpg element to the series it quickly became one of my favorites, with SOTN being at the top of the list.

there are a few games that I will beat at least once a year, those being:
Castlvania: SOTN for the PS
Castlevania: AOS for the GBA
Crystalis for the NES
The Original Final Fantasy for the NES, though I find that the Port/Remake of it to the GBA in the form of Dawn of Souls was a very nicely made work.
Dragon Warrior 1 for the NES

All of the Mega Man X games...

the Sonic games are the ones I'm addicted more than any other game

I'm really addicted with is "Super Mario 64", I found it addicting trying to get all those stars in each level.

Most addictive to me have been Civilization IV, Borderlands and Dead Island. Also one other game I sometimes play because I like it a lot is Impossible Mission for the Commodore 64.