First, some unexpected that I think may occur:
Microsoft will announce and unveil a slim verison of their X-Box 360, hoping to boost sales in Japan and hopefully create more appeal in Europe. It will shipped with an exchangeable exterior which can be swapped with shells sporting various decorations and/or artwork.
Mass Effect 2 is shown briefly at E3 along with an announcement that Mass Effect 3 will be episodic. Along with this, a slew of downloadable content for the original will be shown/announced.
Sony will introduce (yet) another SKU sporting a big HDD and full software emulated BC. This will fall into the 350-400$ category. Their 40GB will be reduced in price, and may drop an entire century in pice, in two primary phases; MGS 4 and Gran Turismo 5 launches.
A playable post-beta of Killzone 2 will at E3 and the full game will launch in early fall (september). Moreover, the game will recieve average reviews far exceeding most expectations (in the 9's).
Polyphony Digital will appologize for not including more cars and tracks from real life in GT5, but will redeem themselves by commiting to making big downloadable packs of cars and tracks released every 6-12 months.
Nintendo will ramp up the production of the Wii, but by a significantly smaller amount than expected due to a slight case of company timidness.
Diablo 3 is unveiled, and turns out to be an MMO much to many fans' sorrow...
Some expected happenings of 08:
A first peak at Gears of War 2 will shown at GC in Leipzig.
The Elder Scrolls V will premiere a sneak peak at the same happening along with a "timed exclusive" tag.
Kojima Productions and Konami will announce an MGS game filling the gap between Sons of Liberty and Guns of the Patriots starring Raiden and Meryl as playable characters. This title will be multiplatform (Wii, 360, PS3).
Civilzation V will be shown at E3, featuring an entirely new and unused interface solution (since Sid Meier himself is working on it, it will be amazing).
Starcraft 2 will be launched with a giant Blizz-fest and the first annual World Championships in Korea are allready dated... 
Fallout 3 will arrive in November and will be tagged as a "timed exclusive" for 6 months (360).
Half-Life 2: Episode 3 arrives in October and a downloadable teaser from Half-Life 3 will become available on Steam.
Bioshock 2 will be announced and possibly featured on E3, though with a different name.
A brand new Lemmings title for the Wii will be announced and showcased (just a gut feeling).
There will be more events, of course, but I'm tired of typing... 
What are your expected and unexpected events for 2008?
