Q: Why won't my photos come over as RAW? They only came over as a JPEG.

Do you see this J symbol in de lower left corner:

because -in that case- Photos has imported both the RAW and JPG (assuming that you shoot in RAW+JPG just like I do).

Unfortunately, Photos does not distinguish sufficiently between RAW and JPG, although one can use the RAW format for editing.

I had to change my workflow, as described here: How to import only JPG (i.e., leave RAW on camera)

Further, it will depend on your camera model, whether Photos can read your RAW file. Check for supported cameras here: OS X Yosemite: Supported digital camera RAW formats - Apple Support

If your camera model is not listed, you might want to ask Apple to include it: http://www.apple.com/feedback/photos.html

Now... I wouldn't edit RAW files myself in Photos, never did that in iPhoto either, but if you want.

1. Doubleclick the file bearing the J symbol at the bottom left as in my illustration above;

2. You will get an enlarged picture. Now click the < Edit > button at the top right of the screen, this brings you into the Edit-mode;

3. Now, from the Image menu, pick "Use RAW as original":

There you go...