I guess I haven’t been playing the right ones, because lately I think they all suck. So what is your favorite game and why is it your favorite? YOU ONLY GET TO CHOOSE ONE.
As for my most favorite game (or series for that matter) is something that a lot of you are very familiar with! 
It is the “Monkey Island” Series, published by Lucas Arts (called Lucasfilm back in the day). It was originally thought up by Ron Gilbert, and the original was released in 1990 on floppy disks. Reason being, it was a DOS game (many of which i still play today!.. that’s right “old skool!”)
Anyway, Monkey Island is a point-and-click adventure game that took on the theme of pirates. It has a very interesting story that would force you to stay put, in front of your computer (no matter how badly you needed to go to the bathroom! lol!) The game is overflowing with great humor, for people of all ages. However, the game-play in the original games is what makes this so unique compared to all other games (and genres for that matter.) The first game of the series, “The Secret of Monkey Island”, the main character moves using the arrow keys, however interacting with other characters and elements requires the player to select a command (as shown in the screen-shot below.)
Overall, I could go on for days about this game and its series :P, however I strongly recommend this to everyone (even if puzzle games aren’t your thing or you simply… hate pirates!), I got a gut feeling you may enjoy it! but, be sure to play the DOS version in 16bit color to get the real experience!
If I sat down to carefully weight wich game I have played has the best all-around story, gameplay and effects, I’d take a while to decide. But going by the number of times I’ve played it (5 at least) I’d have to admit that my favorite is- Final Fantasy V!
This game gets underlooked because it doesn’t have the memorable cast that other FF games do (though it DOES have its great moments, like Galuf’s heroic death) or the best story (though it does have some original ideas, like the whole merging-planets thing) and it SURE doesn’t have good graphics (they could’ve spruced them a little for the Game Boy Advance version, meh) but what keeps bringing me back to it is- the Gameplay!!!
You start with the ability to changes Jobs (character classes ) AT WILL. So you can have an all-Ninja party if you want! And you gain more classes as you go. And there are hidden ones to unlock! (I tend to spread them around, for example Batz gets all the fighter classes, Reina gets all the spellcasting ones etc.) And every class has several abilities to earn over time, AND you can combine the abilities of different jobs for some incredible combos!!! (I often try to finish the game using only special abilities and no spells.) And then there’s the imaginative bosses, the inventive dungeons, etc. (the pyramid is a headache with all its undead monsters, unless you obtain the Bard song that kills them.) And the story never stops flinging you from an incredible event to an even MORE incredible event, etc. The last time I played I cheated with a code device because the GBA has a Job that is only available after you beat the final optional boss- by which time the game’s pretty much over, bah! So I got it from the start with the code. 
Heck just thinking about it makes me want to play it again!
As hard as it is the to choose, my all time favorite has to be Final Fantasy VI. It was the game that brought me into the series and the RPG genre. It wasn’t my first RPG either, Breath of Fire was. I’ve completely memorized the the opera scene and I still say Kefka is the best villian ever. Well, that and I must have replayed the first half a dozen times with the Paladin Shield Game Genie code. The funny thing is that I never actually finished it untl I bought Final Fantasy Anthologies (V and VI) for PSX. Oh, and back then, someting about a pink haired naked troll chick turned me on.
So, if my favourite game is Galaga, would you really like it? Anyway, here are a few suggestions, by genre.
Super Mario World remains one of the best platformers of all times. Have a good controller. Fun, tight controls, great gameplay.
Metroid Zero Mission is a gba remake of the original game + worthwhile extras. It’s short, you can break sequence and do stuff in the order you want and it’s fun. Play Super Metroid if you you prefer getting lost.
Starcraft is still an amazing strategy game, lacking only some newfangled interface frills. It has a good campaign if you’re into single player (the first couple stages may be slow) and it has a great balance between the three races. If you get hooked into that, Brood War is one of the best game expansions with great plot and stages. In fact, I finished the campaign of SC2 and will be probably reinstalling Brood War.
Tetris. Tetris is an euphimism for addiction. Just choose a version with good controls, perhaps a customisable one.
By the way, if you look into Monkey Island, choose the second or the third game. The humour is far better.
And if you want an rpg, go play Fallout 2 (and persevere through it’s silly intro dungeon). Post-apocalyptic game, freedom to create your character as you want and have your choices affect your gaming style. These forums are full of posts on why FO2 is great.
Yadda yadda yadda
Megaman 2. Combination of solid gameplay, controls, crisp graphics and sound easily make is a game that isn’t good through the sheer force of nostalgia goggles, but by it’s own virtues. Stands through the test of time.
Rigmarole, you are disqualified.
I’m sure NOBODY else here has played it. But it is a lost gem.
THE PLOT:
Basically you and your crew have been stranded on a planet for 30 years or so, and since you’ve been gone, the earth has been surrounded by a force field. And most of the galaxy has been taken over by the Ur-Quan, a species that wants to bring order to the galaxy. So anyway, your job is to do missions to get other aliens to join you in your fight against the Ur-Quan. It is a very entertaining and addicting game. It’s funny as hell. Do it. Download it now.
Smash Brawl.
So long as I don’t fight against anyone who’s super hardcore into the big-league fancy-schmancy bullshit.
Would’ve been Guilty Gear X2 series, but I don’t have anyone much to play against these days to call it my absolute fav.
Ikaruga.
Not gonna choose, but if I choose one I will automatically list five more to go with it.
Street Fighter 2. That is probably one of the only games I could seriously never, ever get tired of.
Who is your main?
Thread’s done after this guy. FFV is the best.
In terms of my absolute favourite video game… well that’s simple: Frogger.
Runner ups:
Chu Chu Rocket
Earthworm Jim
Super Metroid
Starcraft
Tetris
Street Fighter 2
Depends on the iteration. In the much earlier ones, I preferred Guile, but in the latest versions of SF2, I main Chun-Li. I can still use anyone pretty well, though.
I played it many years ago, I finished it, and I think whomever came up with those blue-skinned acquatic girls who battle in space in dildo-shaped ships is among the sickest videogame producers ever.
I loved the culture of the rhino-people, though.
There have been good video games recently, it’s just a matter of trying everything new. My favorites nowadays are the Left 4 Dead series. In a market that’s over-saturated with zombie massacre games, this one stands out because of the cooperative play. And by cooperative, I do mean it. It’s more a game about teamwork than it is about a zombie carnage fest.
Similar in idea, there’s Alien Swarm, a free game. It’s fun, the only thing that upsets me about it is how short it is. And despite the differences in setting and gameplay when compared to L4D, the essence is still the same: teamplay against an enemy that’s got advantage in numbers.