From a few months with an Olympus E-PL3 (last generation, I know) and a pair of lenses - yes, but not yet.
For the bulk of what I do, the Olympus has real advantages over my Nikon D7000. It's much easier to carry round and so gets photos by simple virtue of presence. The ability to shoot waist-level on the screen is a major win, as is the ability to actually see sensor response live. No more guessing dynamic range and chimping, it's automatic.
It's not there yet though, and neither are other mirrorless I've handled -
* Many fewer direct controls. Simple things like changing ISO or switching AF off are just fiddly.
* I've tried shooting moving subjects - it's just not as good as an SLR, you can't pick up and hold a subject anywhere near as quickly and easily.
* System scale. None have a flashgun as good as my Nikon SB800 that I've found. My ultrawide SLR lens is double the price. Only Fuji (well, so far) seems to have really got quality fast glass in any quantity. Nine have significant third-party support currently.
We're at a cross-over. In a few years the scene will look very different and mirrorless will be the way of the future, but none of them are ready to take over from SLRs properly yet, I'd suggest.
The Sony alpha line is moving agressively in that direction, and that includes all the nice glass and other bits of a system going back to the very first autofocus SLR (Minolta's). The lineup today no longer has SLRs they are all SLTs, with a fixed semi translucent mirror just for the phase-detected focusing system. The optical viewfinder was replaced by a screen fed from the sensor.
The (very well confirmed) rumors are that they will be doing away with the mirror completely, and going full mirrorless. Without the mirror there the extra space should allow for all kinds of fun adapters to other systems.
Their existing mirrorless sytem (NEX) is also moving fast. They are about to announce a SLR-shaped camera and the rumor is they will be moving NEX to full-frame and adding in-body antishake at the same time.
When it comes to high-end mirrorless Sony is the one to watch.
Willing to be persuaded otherwise, but the major win of mirrorless for me is scale. A mount can lose its mirrors but the flange distance is still based around a mirror box so there's no win there. NEX is nice in some ways but I'm not convinced the site difference with a standard kit zoom mounted between an NEX and a Nikon D3200 is worth a system switch.
NEX currently sucks because it has no good compact lenses, so as you say I don't see the appeal of it versus a normal SLR. For me the real credible story of a good mirrorless system would be something that I can mount a fast small prime to and have a compact kit and yet also have the option of mounting a 70-400.
For the alpha the mirror box space being empty is a huge gain for people that want to make adapters. Suddenly a Nikon adapter becomes possible when before it wasn't because there simply wasn't enough space. If I was Sony I would do the alpha mirrorless by keeping the same mount but moving it back, removing the mirror box space. Traditional lenses would be mounted with an extension tube to mimic the mirror box distance and you could build extension tubes that switched the camera mount to Canon/Nikon/Olympus/whatever.
For the bulk of what I do, the Olympus has real advantages over my Nikon D7000. It's much easier to carry round and so gets photos by simple virtue of presence. The ability to shoot waist-level on the screen is a major win, as is the ability to actually see sensor response live. No more guessing dynamic range and chimping, it's automatic.
It's not there yet though, and neither are other mirrorless I've handled - * Many fewer direct controls. Simple things like changing ISO or switching AF off are just fiddly. * I've tried shooting moving subjects - it's just not as good as an SLR, you can't pick up and hold a subject anywhere near as quickly and easily. * System scale. None have a flashgun as good as my Nikon SB800 that I've found. My ultrawide SLR lens is double the price. Only Fuji (well, so far) seems to have really got quality fast glass in any quantity. Nine have significant third-party support currently.
We're at a cross-over. In a few years the scene will look very different and mirrorless will be the way of the future, but none of them are ready to take over from SLRs properly yet, I'd suggest.