GS2 vs N9 is actually an interesting face-off, because if we put application support aside for a change (you can prefer almost any other phone over the N9 if that is your priority), this really comes down to one thing:

Are you all about specs or the experience? This pretty much goes through the entire spec list:

CPU (+Battery)
GS2 has the faster CPU, but N9 UI is at least as responsive and has no additional Java layer. In other words, the N9 does more with less. But the GS2 still packs the brute force, if you require it for a specific reason...

Screen
Bigger is not better in mobile phones... So it is weird to book this as a GS2 advantage. The N9 has a huge screen for its form factor, easily beating the iPhone which comes at a comparable form factor. Not to mention the slightly higher resolution on the N9.

Tablets are not superior to phones because they have a larger screen, they are just different. And so the GS2 is different as well.

Shape
It is true the the GS2 is thinner at its peak, but what does that really matter? The N9 doesn't look nearly as thick as its spec makes it sound like (which is already fairly thin), due to the curved shape which tapers out at about 7mm on the ends. The peak of 12mm is only reached at the very center of the body. Furthermore, everything is smooth and rounded, which means that it fits perfectly in the hand and slides effortlessly in and out of pockets. It got the looks and function, what more could you possibly want from it?

The GS2 is not nearly as comfortable to hold with its hard angles, even if it wouldn't be as big as it is.

UI
You already know about that. The important thing here is not that MeeGo is a pretty cool foundation, or that the Harmattan UI does a few things here and there more elegantly than Android. The really important thing is that it was developed in conjunction with the hardware, and takes full advantage of its ergonomic properties. The most obvious being the swipe gesture with the curved, beveled screen and button-less front, which is a killer feature in itself.


Bottom line, if you just look at the numbers, GS2 beats the N9 hands down. If you actually use both devices, the story is very different. So you get to choose between specs or experience.

And for this reason, I strongly suggest everybody (who is looking for a phone like the N9, not a more tablet like device or an app ecosystem) to wait until it is out and to see what reviewers have to say about it after using it for a while. This is not something you can properly evaluate just from reading the specs.