S2 lens is very very good? its good, but not that good. It still can't replace a good camera.
besides, GNex doesn't take terrible photos either.

depends on individual preferences, slightly better image quality vs zero shutter lag?
if you're serious in photography, get a real camera.
if not, you're gonna use it for "casual social sharing photos" anyway, and zero shutter lag would be the better feature here.

faster GPU is irrelevant when the "faster" doesn't bring any significant to the user. What does that faster GPU brings? higher benchmark?

Gorilla Glass is just a brand for fortified glass, GNex is using a fortified glass too, just unbranded. iPhone doesn't use Gorilla Glass too, does that mean iPhone's glass gets scratch easily?
Plus that doesn't mean your glass doesn't scratch, and if you do apply screen protector, this is a moot point.

I am guessing you don't really know what's a Nexus phone? its the developer phone for Android. Even at the first month of release there has already been tons of developer support. GNex toolkit that does every hack you can on Android in one click has been developed in a month time.

and you're saying that GNex's design is funny. I see it as sophisticated futuristic with that block monolithic look, void of any brand at the front gives it a clean and minimalist look, couple that with that slightly curved form factor that makes it looks so sleek, it's something different from any other Android phones. S2 on the other hand, looks like an iPhone knockoff. Not a bad thing, it looks good and its practical so why not.

I am just bringing another perspective that doesn't just look at paper spec. Not saying Nexus is a definite better phone, because S2 does has its own advantages too, SD card slot especially. But this is obviously two different flagship phones, one is Google's flagship, another is Samsung's flagship. It's up to your own preference on which is better. Does Google's direct software support for the Nexus line appeal to you? If not then its just another Android phone, in which S2 might appeal you more if you're more of a hardware only kind of guy. Plus, the price of S2 is significantly cheaper than Nexus as of now, with similar spec (better for some) of the Nexus, making it a really good choice. Let's just say either phone you choose, you still win, at least that's how I see it

S2's 2MP, Nexus's 1.3MP. But afaik, Nexus is capable of 720p recording, while S2 only does 480p. I could be wrong, please correct me if I am.

which one do you think will win in terms of front camera?

1.3MP with 720p recording or 2.0MP with 480p recording?