I purchased an M7 earlier this year to replace my M6 and M8. Main motivation were the MP finder and AE. I also owned Contax G2 and Zeiss Ikon, and currently use also an unmetered CL.
This review I find sums it all up nicely:
http://www.imx.nl/photo/leica/camera/M7/M7_start.html
I can understand those who do not feel the same fascination and sentiments for the M7 than to the more classic bodies, it is a little like that for me too.
The reality is - it is the best camera I have
used, and it is the camera I would use over any other when it really counts. It is a work tool - smooth, precise and reliable.
The AE makes it faster than the M6 even if you use it like a M6 (AE lock) in difficult light situations. The shutter is quieter then the ZI, M6 or M4. Whether that matters is up to you, to me it does - it is the reason number 1 I prefer it over the (really nice) ZI.
The MP-finder is clear and virtually flare-free. DX reader...no idea, I always set the ISO myself anyways. Batteries fail, sure. The mechanical times are nice and help through the crucial times until you can replace batteries (reason nr. 2 I prefer it over the ZI). I carry a lightmeter all the times anyways. M6 batteries fail too, and more often than I thought and expected it.
Main drawbacks: Not every repair shop that can service the mechanical Ms can/will/wants to service the M7. If it needs to go to Solms when an M6 can go to a more local shop. This may or may not be true depending on where you live. The camera feels a trad too heavy and tall when you come from a M4 or M6. But so does the M4 when you come from the CL.
I am not convinced that the mechanic Ms are per se more reliable then the M7. The cameras that required no repair or CLA even after hard use were my Contax T3 and G2 - and they are a lot more "electronical" than the M7.
Not sure how I will feel about the M7 down the road. I used it heavily this summer in the Caucasus both in the high mountains and for documentary work - both applications I used the M6 before. The M7 is fantastic.
I thought about an M4 or M4-2 instead to finance an M8. These thougths come when I have too much time to think about gear than time to use it; but I looked at them (M4 and M4-2), handled them, tried them...no love. When I use the M7, all doubts vanish. Of course, this is subjective. Since I have the M7 I do not miss the G2 anymore (that means a lot).
If I want it light and simple - CL and Contax T3. If I want a film work tool that works, is fast, precise, discreet and reliable - M7.