Here my impressions after using the GH2 for some days. Please note that these are my personal impressions about this camera and are by no means scientific or a real review!
Let me start with comparing GH2 to other DSLRs first. I also own a Nikon D700 with several of the high speed 2.8 zooms from 14-200 in total focal length. There is NO DOUBT that the results from the D700 would have been better at all ISO. But how much better? Maybe 10 or 20%??? Definitely better WRT ability of printing larger at higher ISO images, so of course you can see the impact of the 16MP 43 sensor. Given that I want to use the GH2 on business trips or for casual photography the results are topping my needs in any case. And I would not have liked to carry my Nikon gear (nor Hasselblad) instead of the GH2. Or a Leica M9 - but this is a different story and I do not want to get into RF versus EVF discussions now.
What about other small APSC DSLRs? The most comparable would be Nikon D7000, Canon D60, Pentax K5, Sony Alpha 55, etc.etc. Well why did I not simply buy a D7000 and use some of my Nikon glass or add some of the great Nikon DX zooms? I asked myself several times before I choose the GH2, simple answer is that the GH2 form factor, size and weight is considerably smaller and lower compared to a Nikon D7000 (or K5 or even A55). Now would I consider IQ better from one of these cameras, as they have a larger sensor? In the area between ISO160 - ISO1600 probably not, at ISO3200 maybe and above ISO3200 for sure, although not very much IMHO. As you can see from my posts in this thread, one can nicely survive with ISO3200 and I could also have used ISO6400 or 12800 on the GH", although I so far had no real need (great IS of the 14-140). And be honest - back n film days I was happy to have good ISO800, so working ISO3200 are already a big leap forward.
As some of you might have noted I also shot a K5 for some weeks before I sent it back. This was not because of bad IQ or bad high ISO, this camera was really a great performer WRT IQ under several circumstances. But there was one main reason why I did - it was not so well and reliably working AF in some conditions, mainly of course low light, but not exclusively. I never found any AF unreliability in the GH2, only thing that can happen is that it is too dark for contrast AF, but then the GH2 will simply NOT do AF and leave you with MF, so you know about it in advance. Not like the K5 which did some focus, approved correct focus but then it was backfocused (in my case).
Which brings me to another major part of the GH2 - the EVF. I should say that I am an old Leica (R and M) guy, so I love good viewfinders
I could not get friend with several EVFs (G1, GH1, A55, and some others) so far, the first one which triggered satisfaction was the one coming with my EP2, but the EVF in the GH2 is again a milestone above that. Not in resolution, but in smoothness when you move the camera or at larger focal length, because the sensor is read out I think 120 times a second and the image of the EVF is refreshed 60 times a second in the GH2. So this results in a very smooth looking picture. Could this be improved? Sure there could be always improvement and before EVFs will be able to get used in Pro DSLRs there needs to be another improvement in my eyes, but I would think this is not too far away. For a camera like the GH2 which I would rate as a high end consumer camera, the EVF is absolutely perfect. And I prefer it to a OVF found in comparable DSLRs like mentioned above, because their OVFs tend to be so small (even if the are 100%) that MF will not really work under bad light, which is not an issue with the GH2 EVF, especially when you turn on all MF support in the menues.
I would dare to print up to 50x70cm from that camera, you have 16MP and they are very good to good quality, so especially when printed you will not see much difference even to a D700. WOuld a D3X do better, or a A900? Sure, but again then you would carry 5 (or more) times the weight and size and get maybe results which are 20% better? Or 30? Or maybe only 10%? Who can answer that????? I can't and here you see the reason why I think that a camera like the GH2 has become already so good that choosing it will not impact lot of the quality - really visible quality - in this type of leisure and travel photography.
If I really needed high IQ, I would take my H3D39 and lenses and blow anything away. Or upgrade for the price of 10xGH2s to a H4D60 and be even better in blowing away
Or go for any of these S2s which are currently working if I had the luck to get one - for even higher amount of money. But would I want to carry these beasts around? Or bring on a flight with luggage restrictions???? NO DEFINITELY NOT!
Short answer her: in my eyes the GH2 has reached a level of maturity, that it is on the same level as a APSC DSLR or even better in some regards, and already very close in my eyes to a FF DSLR, but MUCH smaller! Comparing to MF does not make any sense. So for me this is an ideal travel camera, maybe add 1 or 2 M43 lenses, maybe even a higher speed prime, and you will be satisfied. Or use it as a complement to an existing MFD system, just to have something to shoot high quality around anything you shoot with your MF gear.
Hope that helps for now. I so far love my GH2 and do not regret having bought one!