Of all the many things I would call it (excruciating?) boring is last!
I started 6 months ago, I shuffled rather than walked for the first several weeks because I was so sore (had to grip the sink to sit down to the loo, etc).
The first amazing thing you'll notice is your arms. 3 months in, they started looking really toned. I'm so happy with my shoulders/clavicles/arms that I have been in sleeveless and spaghetti strap tops the whole summer. My shoulders are really hard to the touch.
Now (6 months in) my stomach, which remains a bit flabby, has what I could only describe as a ring of muscle around my belly button emerging. It's like a circle, the size of a big pancake or small frisbee.
I can feel the muscle in my legs, but that is not so easily exposed - I'm running 3 miles, 5 times a week and my legs have toned up a bit but I still can't see the muscle that I can feel.
I'm 44 by the way, and was a size 12 before I started all this and am now an 8-10. What I also discovered is that because I held my fat in all the usual middle-aged ways i.e. love handles, and had adapted my wardrobe to that, my clothes carried in fitting in the same way for a long time - skinny jeans, for example, will accommodate the ring of fat above so you won't have the satisfying gaps in the waistline that you're looking for (those have only just arrived in the past month or two).
The scale is not your friend in the case of pilates, before I could see all these effects I saw that I had gained about 6 pounds and it threw me into a terrible state. I suggest having your body fat measured in advance so you can see the results objectively.
My best advice, though, is to find a 45 minute rather than 1 hour class. This made all the difference in the world for me. I prefer the mat pilates to the reformer and it's a helluva lot cheaper - I can't find reformer classes for less than £25 (west London) but I've found a lot of intense mat classes that are unlimited for say, £70/month.
Good luck.