Guitar Hero and games like it are behind the Christmas boom at US video game retailer, GameStop.

The company has raised its quarterly earnings estimate after a sharp rise in holiday season sales.

However, following on from the announcement, shares of GameStop fell 6% as analysts cited their concerns that video game sales could not maintain their momentum over the short term.

Mike Hickey from Janco Partners told Reuters that the key difference with last year's sales was World of Warcraft which sold 850,000 plus units in January.

He continued, however, that, despite some pessimism over how long sales can continue to e high, traders seem to be generally confident about the US retailer. "...We continue to like the name. They appear to be doing all the right things", he said.

GameStop's comparable store sales for the holiday period for this year and last increased 20%, while total store sales for the period rose 34.7%.

Given the sales increases, the retailer increased its fiscal fourth quarter 2007 comparable-store sales estimate from a range of 7-9% to a range of 15.5-16.5%.

Full-year earnings per diluted share are now estimated to be 13 cents per share higher than guidance issued in November, continues Reuters.

GameStop listed the top five video games sold during the holiday period as Activision Inc's Guitar Hero III, and Call of Duty 4: Modern Warfare, Ubisoft's Assassin's Creed, Electronic Arts' Rock Band and Nintendo's Super Mario Galaxy.