Sorry, I've got to go with sales here. Saying that you have to have a certain percentage of the total consoles out there in order to be a success is ridiculous. That means that no niche title can EVER be considered a success. And once you reach a certain number of consoles sold, it's guranteed that there will be a certain level of diversity which will make it impossible for ANY game to be considered a success.

No, only profit can really be considered a good estimate. If you manage to make the game on $1m and the games sell for $30 then then even just 5k in sales would be a solid success.

So the PS2 had no successful games? Ok ...

Ultimately, the success of a game can only be determined on a case by case basis with the deciding factor the return on investment accounting for the opportunity cost.

If a low budget game can sell about 250,000 copies and a high budget game 500,000 copies WW.

There are all kinds of factors one should consider, sales, profit, artisitc and fun-value.

And they arent the same around the board.  For instance, if a third party sold 500,000 on Wii that would be a huge success, but if a Nintedo game sold 500,000 that would be a horrible failure.

For attach rate, 10% would be quite successful in my eyes. That would mean that 1 in every 10 console owners own that game (right?).

But this theory doesn't work for every game, especially those on the Wii. Hardcore games on the Wii have to sell to a lesser hardcore audience than the PS360. The many moms who own a Wii aren't gonna buy Metroid Prime.
So on Wii, any game over 600 000 is a success for me. While for the HD consoles, 1 million seems like a good benchmark for measuring success.

From a developer view, a game is successful once you've hit the profit margin, having made up all the money in development. Of course, if you have a publisher, then its the break point that the publisher starts sending money to the developer after the game launches.

Depends on the game ...

On one end of the spectrum you have a very low budget niche  title with no marketing that is profitable after 50,000 units sold, and at the other end of the spectrum you have a big budget HD game that has a major marketing blitz which requires 4 Million sales to break even; if they both sell 500,000 units one of these games is a smashing success whereas the other is a massive failure.

For me, a million= hit.

Most companies would likely be satisfied with 500,000- 750,000.

1 million hands down!

If it's profitable