A lot of users swear by full frame cameras reasoning that depth of field can be mastered best with this format. True, DOF can be better achieved with this format but it all depends what you shoot. Landscape photographers try to get MORE DOF rather than less. So that argument doesn't hold up all of the time. It also doesn't mean that it's impossible to achieve a shallow DOF with other formats. I personally use many different systems with quite different sensor size and I have achieved shallow DOF with all of them. If I can achieve that then anyone can.
Right now my preferred camera system is the M43 format. I think they offer the best quality for what you pay. The cameras are fast, small and lens selection is just terrific (especially with the introduction of the Olympus 300 f4 and the Panasonic 100-400 f4-6.3). That's 800mm reach with the Panasonic. Incredible in such a small lens. Reviews are also good. Granted it's rather slow at the long end but then again it's not intended to be used indoors.
What actually drew me to this format was the Panasonic L1 which I fell in love with the moment I held it in my hand. I didn't buy this camera when it came out because it was terribly expensive, so I waited a couple years and bought one from a well known auction site.
It's built like a brick outhouse and it just keeps on going. It just works, whatever happens to it. It's has quite a few hits and knocks over the years. Great quality. The L1 is of course a 4/3 camera but the newer M43 cameras use the same sized sensor. The only difference is flange distance between sensor and lens. This allows for smaller and lighter lenses and they definitely are smaller and lighter. So the moment Panasonic brought out the GF1 I knew I would buy it. And I wasn't disappointed either.
The 2 lenses I used on the L1 the most were the Panasonic 14-50 f2.8-3.5 kit lens and the one pictured above, namely the Panasonic Elmar 14-150 f3.5-5.6. (35mm = 28 - 300mm). Just wished it was a little wider. Granted the 14-150 Elmar isn't a particularly fast lens but I know for a fact that I can shoot at all focal lengths at all apertures and get constantly sharp images. There isn't one focal length that isn't sharp. It's just a great all round lens. Superb image quality. Although the L1 is only a 7.5MP camera it's really amazing what you get out of the files. I've actually printed a 180cm x 120cm print and that's after cropping to a 3:2 ratio.
I've seen the Elmar 14-150 go on ebay for around €450 and the L1 kit lens, the 14-50, go for around €200. These are bargain prices especially for the 14-150 that also works extremely well on the M43 bodies via adapter. The only problem with it is it's weight. It does make the smaller cameras rather front heavy but once you get used to it, it shouldn't be a problem. Of course if you're thinking about this lens you have to factor in the price of the 4/3 to M43 adapter.
The only reason I purchased some M43 cameras is well.........technology has advanced a lot in 7 years (L1 came out in 2007). The modern cameras such as the Panasonic GX8 and the Olympus E-M1 do have better functionality and they do most everything better. But we all know that functionality isn't everything. Sometimes I tend to bond with a camera and this is exactly what happened with the L1. I still use it sometimes today but I must admit I do feel the weight after carrying it around for a few hours. I would rather carry around a GX8 or an E-M1. They are lighter and I'm not getting any younger 
. Weight is definitely a factor these days when I'm selecting a camera. That was something that didn't factor in a few years ago. Reading around the Internet I find a lot of photographers are glad that these cameras are on the market, because they have the exact same problems as myself, namely age.
Coming back to M43 cameras, does anyone even remember the Panasonic GF1 or the Olympus E-PL1? They were extremely versatile cameras have given me a lot of pleasure over the years. Both had a 12MP sensor which was/is quite adequate. The E-PL1 was a little quirky for some functions but the output was and still is excellent.
Images from the Panasonic GF1
The following might be a little small by today's standard, but you get the idea I think.
Images from the Olympus E-PL1
Then Olympus came out with the E-Px series of cameras (E-P1 was their first camera). I hated the E-P1 when it came out. Give me camera without an EVF and I'm totally lost. I will never again purchase a camera without one. Never ever. The E-P2 was an ok camera but the big improvement for me I found was with the E-P3 and it got a lot of use for a year or two. That's when I stopped using the E-P series. I found the external EVF was starting to bother me.
The Panasonic GF series carried on but I wasn't interested because you couldn't even fit an EVF to those, even a bad one like on the GF1. One good thing about that EVF was that you could use it also on the LX5 which I did and still do occasionally. I'm not going to go through all the models here, suffice to say that the Panasonic GX7 and GX8 are tremendous cameras. Very capable as well as the Olympus E-M5ii and E-M1. There is no such thing as a bad camera today, it's just a matter of preference. One photographer might prefer the ergonomics of one model over another, or prefer one sensor over another. What's important is that the colours are to your liking. It doesn't matter which camera you use, you just have to bond with it. If you don't bond from the first couple of weeks I don't think it'll do much for your photography. If you don't get on with it, ditch it. Just sell it and move on to another one. Find one that you like using and it will let you concentrate on your photography rather than the camera.
Before I end this post I would like to touch on two models that have impressed me quite a bit. Both are Panasonic models, namely the LX100 and GM5. Both are small containing the normal M43 sensor and both have impressed me with image quality. The LX100 has a bright fixed lens which I have used quite a bit indoors too. The GM5 I took with me last year to the south of France for a 3 week holiday together with the 12-32 kit lens and the very small 35-100 f4-5.6. Please don't get that mixed up with the f2.8 version. Those two lenses gave me a 35mm equivalent of 24 to 200. Ideal for me. The GM5 has impressed me so much that I've just bough a second one. Not new, but in nearly new condition. I'm going to put the 12-32 on one and the 35-100 on the other. You can't really get any smaller that thet. You can't really tell that you have them with you. If you haven't looked into those two cameras please do. You'll be surprised by the output. Take a look at my photoblog. I have quite a few images posted there with both cameras.
And to finish, some images from the above mentioned cameras. Enjoy.
Images from the Panasonix LX100
Images from the Panasonic GM5
