To clear things up, MGS4 is NOT coming out for the 360. That's been established a looong time ago.
Since no one seems to really know that, it's hard to take most of this thread as credible.
Anyways, the only thing going for the 360 now is GoW and Halo 3. Honestly, that's all anyone cares about. It also had a crappy launch. From what I've heard, online is excellent, but it costs money (though it's reasonable).
The PS3 has Resistance right now (blows any launch 360 game away), and it's excellent. Other than that, it also had a crappy launch. But, the system has an extremely promising line up with GT, FF, MGS, etc. Online is actually pretty good with PS3. Sure, the PS3 store has slow downloads, but for being brand new and also free, that's expected. Playing Resistance online is fast and easy. There's always people to play with, and I've never seen any lag. For being free, that's great.
Whether or not Blu-Ray lives (it's technically more impressive, but that doesn't matter), the PS3 games will still benefit from the extra space. I'm sure you'll see that put to good use within a couple years. Still, I enjoy being able to watch Blu-Ray movies on the PS3, because they are awesome. The 360 does not benefit from anything more than the now small capacity DVD. That's fine for now, but I think the extra space will get at it later. And the HD-DVD add on, it's nice that it's optional, but they'd get more out of the system if they put that towards games.
I've played all 3 of the new systems. Honestly, I think the Wii is cool, but it only has Zelda. If anything, it will only be worth having for cool features (controller, downloading old games, features like forcast, etc). The 360 is impressive (and has better online), but no games have really made it worth buying except GoW (and eventually Halo 3). With more support though, it has a promising future. The PS3 also has a promising future, with the Blu-Ray, motion sensing (Wii is a lot better there though), exclusive titles, etc. Playing Resistance and the Motorstorm demo is great.
Honestly, they're all good systems. Personally I think the PS3 will end up with the best sales. I personally enjoy the PS3 more than the other systems, but that's just me. I think too many people have these weird negative feelings towards Sony and PS3...just grow up and accept all three consoles. If you can't, well that's just more fun for me.