I'd think a few more copies need to be sold to be considered succesful.  I would think a game needs to turn a profit, not just cover dev/advertising costs.  I'd think a company that creates games that are only capable of meeting dev costs would lose investors and publishers really quick.

If a game sells less than 30 million then it is a failure.

making a profit is the most important thing. first you must sell enough copies to cover the costs of making the game and getting it onto the market. After recovering costs additional copies of the game sold results in profits to the company.

i think good aswers have already been given

I would say a game these days has to sell a million copies to be deemed a success. Any more than that is a triumph

TADA!

Yep, it's that simple. Profit Profit Profit! There is no magic number for all games that make them "successful". If a game makes money, it's a success. Period.

The level of expected success and the level of success (amount of profitability) may diverge, and that's where developers can be disappointed with performance even if they release a successful product.

That said, most games on the PS3 need > 500,000 copies sold before they break even. Some will need well north of a million copies sold. Some games are a failure at a million copies sold, or two million copies sold, simply because their cost was so high. Some games are a success at 200,000 copies sold.

For example RE4 for the Wii was expected to sell 400,000 units and that would have been very successful simply because it was a port of a game from the gamecube, and probably would have profited at 100k units sold, even at the budget price point.  But the game went on to sell nearly 2 million units so far, making it a massive success for a port that would have cost very little. 

Not all profit is equal. Certain titles are expected to make enough profit to fund other projects. Games like GTA4, SSBB, MGS4 are expected to make obscene profit because their shareholders expect it. Just slightly breaking even would be considered a massive failure.

I guess they have all been failures.

Anyways, for the companies I'd say it is enough to cover costs associated with production of the game.  If GTA only sold enough to cover costs it would probably be deemed a failure by the public.  It probably wouldn't exactly be considered a success by the company, but it wouldn't be a failure per se.

A couple of factors,
1) Did it live up to sales expectations?
2) Did it turn a profit for the game companies?
--How much of a profit?

The bigger the profit, the bigger the success. With the exception being when the sales turn a tidy profit, but still don't live up to sales expectations, people will not always consider it a success, even when it is.

Hmm, interesting question. I've often though that in addition to turning a profit or at least recouping investment costs, which previous posts have covered in depth, there are really two other measures of success for a game.

First, there's success in simply creating a successor, i.e. spawning a franchise of some sort. This doesn't necessarily mean creating precisely the same game over again. The team behind "Ico", for example, went on to create the wonderful "Shadow of the Colossus".

The second measure of success is creating a new type of game-play, which goes on to become the new measure or standard for other games. "Max Payne" revolutionized action games by building bullet-time into its core gameplay; gaming would never be the same.