I'm leaving Sony for last (except for PC games). This post will talk about Microsoft and 3rd party games coming for the Xbox 360 this year and into next year.
Gears of War (Epic/Microsoft, Q4 2006): This was evidently shown behind closed doors, but it seems some people got to see it. I think Tycho put it best today in his newspost today in that this game was an experience and easily the best game of the show. For Microsoft to open their pre-E3 conference with this game was powerful. With Halo not showing up until next year, this is the game that will power Microsoft this holiday. It looks dark and gritty, but it will probably be one of the first games to show off the Unreal 3 Engine. Keep your eye on this title, it is going to be big.
Viva Pinata (Rare/Microsoft, Q4 2006): Yep, many of you laughed at this game, but laugh at this: Gabe says it has "lots of potential" and Bill Harris thinks much the same way I do (6th paragraph). This game is going to be hot for children...red hot. Like Bill said, "Here's one other thing about Microsoft: if Viva Pinata was a Nintendo game, people would be bursting with proclamations about how it demonstrates the genius of Nintendo. That game is going to be huge, and I'm not sure anyone quite realizes it yet." You will soon realize it!
Too Human (Silicon Knights/Microsoft, Q4 2006): Many people had low expectations for this game as well and I think when they actually played it they thought differently. This will probably not be the blockbuster that Gears of War will be, but it will be right up there.
Forza Motorsport 2 (Microsoft, Q4 2006): Yes, it was only shown via CGI pre-rendered movies, but the first game was red hot and I expect this one to be as well since it will be a second generation release. Peter Moore said it would be out by the end of the year, hopefully that is true. In addition they will release a wireless wheel controller, something never seen from Microsoft in the Xbox life cycle.
Fable 2 (Microsoft, 2007?): I can only guess at the release of this game. It was also shown in pre-rendered CGI. I was not a huge fan of the original, mostly because of the length of the game. On the aspect side of things the original was Aces, it just wasn't long enough. Now that Lionhead is owned by Microsoft I can see this game being quite big.
Mass Effect (BioWare/Microsoft, Q4 2006): I don't for one second believe BioWare will have this out by the end of the year given their track record. This game, much like Too Human, is set up as a trilogy. That could be a boon or a curse depending on how you look at it. Given how great KOTOR was, chances are BioWare could strike gold again with this one.
Shadowrun (FASA/Microsoft, January, also on PC): For most people this game will be seen as a tragedy, much like the MechAssault games (although those were good in my mind). Throw away all the things you remember about the original RPG IP and FASA is about to re-write the Shadowrun world. This is an FPS which is pissing a lot of people off. However, if it sells anything like the original MechAssault it will be a big release for Microsoft...they'll just piss off fans of the series and the SNES game.
Alan Wake (Remedy/Microsoft, 2007): Remedy may not have showed the gameplay of this game, but the big news is that Microsoft is publishing and it will only be coming to Xbox 360 and PC. Remedy is a relatively big name in the industry thanks to Max Payne and I hope this game turns out to be everything it can be.
Halo 3 (Bungie/Microsoft, 2007): Just that little 2+ minute demo blew me away. It could have been the musical score or the Covenant ships flying all around, but it got me excited. Post-E3 the news was that the demo was done in real-time and not a pre-rendered CGI. That would be pretty cool if true (as well as put a damper on the Metal Gear Solid 4 showing). This game is the knockout blow for Microsoft if they time it right...an early 2007 release could be devastating for Sony.
Sports Games (2K Games, EA, 2006): I'm putting these all in one. Indications are that each series that saw a shoddy port on Xbox 360 last year is going to see a much better game this time around. Arguably the only sports game to stand out was NBA 2k6 last year, but that was really a graphical upgrade more than anything. Now it seems teams are creating two tracks of games...one for next gen and one for current gen. I think Madden 07 and NCAA Football 07 are the most promising, even though they are missing some features from current gen release (although they are also adding other features) I think they could be big. This could be the year EA makes amends for what they did last year...we shall see.
Lost Planet (Capcom, 2007): Yes, I played the demo and was pretty impressed by the game. If it has a good story I think this game could be a nice little exclusive release for the 360.
Table Tennis (Rockstar, May 22nd): I have not played this game yet, so I don't know what to make of it. It seems the kind of game that will lose its luster after a while, but then again it could turn into a great and addicting game. I guess we'll see in a week. At least it is budget priced (for Xbox 360 that is).
Grand Theft Auto IV (Rockstar, October 16th, 2007): Big news that the Xbox 360 and PS3 versions will be releasing side-by-side and Sony won't have exclusivity on it. Not a big fan of San Andreas, but I loved the other 2 games since the move to PS2/Xbox. If Rockstar can recapture the magic and don't try to balance on the absurd this could be big for Microsoft if the Xbox 360 is ahead in system sales by the time it releases.
I only touch on mostly first-party titles here and I was a bit surprised that Microsoft didn't announce any secret games at E3. In fact, I'm surprised that no one really announced anything of a surprise like they have in past E3s.