This thread has turned out much better than I expected. The thoughtful views have been most enjoyable reading.
Here's what I like about mFT (Mind you, I'll be speaking mostly about the Lumix side of the equation as I have very little experience with Olympus).
1. (Like most people here) The size. In the digital age I was pretty much chagrined by the hefty offerings that seemed like people were hauling an albatross around their necks. I made the plunge into the realm with Leica's Digilux 2 feeling that digital at that time had achieved parity with film. That camera was bulky but not nearly as bulky as DSLRs. Then I saw the Lumix G1. A camera that was small but not too small. But with a thickness (the main part of the body not the grip that's often erroneously included in these measurements) that seemed no thicker than the Leica M6! I was sold. The GF1 and others also had a remarkable form (as well as the Olympus' digital homage to their 35mm Pens and now the OM).
2. The EVF. While there's certainly a love-hate relationship amongst aficionados I am one who loved it IMMEDIATELY. Coming off the experience with the Digilux 2's very 'grainy' EVF (which I thought was pretty cool despite what others felt) the EVF of the G1 was a quantum leap. Did I miss an OVF? A little. But the EVF gave me the equivalent of an HUD that fighter pilots enjoyed with all sorts of information and grids that could be super imposed (or not) over the image providing what I felt was a complete command center while engaged in shooting. Today we're seeing EVF's with resolution and clarity that make the original one I saw in the G1 seem absolutely pre-historic.
3. CDAF. At first the ugly step-sister to PDAF but now fully into it's own. It's blazingly fast. And deadly accurate. And, except in the most extreme low light circumstances is for the most part on a par with the best of PDAF in terms of speed and accuracy. (And for videographers a godsent as the preferred means of AF while filming.)
4. A leftward fully articulating LCD. This addition alone has made shooting with Lumix for me so incredibly enjoyable. Low angles. High angles. Stealthy sideways candid angles. Even self portraits. No other camera approach does it better IMHO. (Curiously I never understood why Olympus had it on their regular 4/3 E series cameras and then ditched it with their mFT offerings.) And speaking of portraits swung out on a tripod, it's like using a Hasselblad or TLR. The live view on the LCD makes everything incredibly facile.
5. A growing line of lenses and then some. Okay, the original lens I got, the ridiculously slow 14-45mm (28-90mm equiv.) zoom kinda sucked. But then Panasonic unleashed the 20mm f1.7. Then a Leica 45 Macro and a Leica 25mm f1.4. Then a 7-14mm f4 (nearly as good as the Oly FT version). And the 14-140 video monster. Then for big game hunters the 100-300mm f4. And now again copying Olympus FT optics offering two fixed f2.8's zooms: a 12-35mm and 35-100mm. Meanwhile Olympus has upped the ante with some nice jaw-dropping m-offerings of their own: the 12mm f2, 17mm f1.8 (which is a better focal length IMHO than Pany's middling 20mm f1.7), THEIR 45mm f1.8 Macro and their luscious 75mm f1.8 (a wow if ever there was one). And if that wasn't enough, mFT opened the floodgates for EVERYONE ELSES's optics from Nikon to Canon to Zeiss to Leica to Tamron to Samyang to Sigma to... And while these are mostly MF lenses the close-up patch borrowed from Digilux 2 days seems to work rather well as the overwhelming evidence on various threads in this section can attest. (Next step: Peaking.)
6. IQ. Initially not too shabby but steadily improving ever since. Olympus and Panasonic seem to have realized that 16 MP is certainly plenty for a good 300 DPI image in a coffee table book or a magazine spread. And every gallery. And with each iteration the one weakness, high ISO noise, has been their focus (pun intended). The OM-D with (I think) Sony's (mostly likely EXMOR like) sensor has been performing impressively at ISO 3200. And there's no reason to think that the GH3 with it's waterproof, full metal MG++ jacket wouldn't be the same. I don't know about you but with Oly's new faster optics and the new sensors I see a grand slam for most situations besides sports and extreme low light PI work with spousal indiscretions. Video, which is not something I'm into, has similarly seen advances that, for the most part, put mFT first on most short lists.
7. Body design. While I mentioned size initially there is a lot to be said for the thoughtful body designs of these creatures. Panasonic and Olympus seem to have struck a right balance of software driven features as well as good old mechanical layouts. A blend of good intuitive menus as well as a careful offering of essential (and apparently preferred by most) buttons and dials and their placement. Realizing that touch screen success in smartphones would have certain advantages (with the right software) in a camera and incorporating them is nothing short of genius. Finally a word or two about camera noise. From the very beginning I've really liked the low-pitched shluck of the G1 and everything after that has been just as non-attention grabbing. Initial reports of the totally silent shutter of the GH3 seem to be a mixed bag. But I'm certain that any issues will be worked out with a minor improvement in the firmware.
Do I find anything to fault?
Probably the two things that any camera with a larger sensor can offer: (1) shallow depth of field. This is simply a matter of physics. And there's nothing you can do about it although SLR Magic's 0.95 lenses can certainly bring you closer. But I've also experimented with the Brenizer method (as Tessalator has as well) which, if you don't mind the extra work of taking and stitching a number of smaller files together, allows you to achieve results that no larger frame sensor could give you (unless of course it's also being used in a Brenizer context) because the lens equivalents simply don't exist (a 28mm f0.8????). And (2) better low light performance. This clearly has come a long way (although I still tend to shoot at ISO 100-360 out of habit) but with others shooting quasars at ISO 12600 it's hard not to be a little envious. (Of course, if low light shooting is your raison d'être for image making you probably wouldn't be using this system anyway!
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(Note there are others but these two are the most glaring.)
So for my money, I really like how far mFT has come, where it's at and if past performance is any indication of future possibilities...where it's going.