I´m not familiar with it in terms of how big it is, how important it is...is it the biggest gaming event in Europe?

I also would like to know.

Decent sized. Not as big as  E3 or TGS. Or Leipzig, I think anyway.

they are all overrated, once it's over fanboys would look up to the next event because of disappointment (example: NO FFVII REMAKE OMG ANNOUNCEMENT LOL)

Not at all and we don't need a FF VII remake, we need a FF X remake.

Sony have a 3 hour conference, and yes it is the biggest event in Europe, it has taken over from Leipzig

According to Sony it's big "gamescom - Europe's biggest videogame industry event." Link

Microsoft had a hard time last year, because Gears of War 2 is banned in Germany.

Was Microsoft even present last year?

Yes biggest in Europe and I expect it to have more atendees than Games Convention (the old one)/TGS had by next year. Maybe even more exhibitors, but that won't be easy.

"With 183,000 visitors, 2,600 journalists and 368 exhibitors from 25 countries in 2006, the Games Convention rivals the Tokyo Game Show as the biggest games event in the world."

I know it isn't Leipzig any more, but still.