Okay, here goes:
the good:
-you'll feel great after you start using it for a while! So great you'll never want to go back!
-you'll see improvements in your altertness, energy, mood, and general health (apnea causes problems with the immune system).
-You'll also find that eventually you will get very used to using the machine and it won't bother you at night.
-You'll feel well rested, have pleasant dreams (no more choking/suffocating dreams if you ever had those before) and wake up less during the night or not at all.
The bad:
-the masks are often uncomfortable and difficult to get used to.
-initially, you'll sometimes toss your mask onto the floor in your sleep!
-allergy symptoms can flare up from any allergens/mold/etc sucked in by the machine. You might have a stuffy nose all the time.
-you can get nose irritation or irritation from straps on your head
-your bed partner might get irritated from the air that blows out of the holes in the mask onto them
-your nose might itch at night from the mask (if you have "nasal pillows")
-you are going to have to do a lot of washing, soaking, and sanitizing of parts of the mask/hoses periodically.
the ugly:
-its possible the mask will always be an irritation and you'll never find one you love (but unlikely)
-its possible you will still have some medical/sleepiness problems that turn out to be due to other causes
-it might work for a while, and then stop working (b/c you need another sleep study due to your pressure needs changing) which might make you want to DIE (I'm in a phase of this right now, need to go back to the sleep doc)
nothing too ugly! By the way, I don't think the dr. is probably correct in saying you'll only have to use it for a couple of years or whatever. I have never heard of this, unfortunately. If your sleep apnea is being caused by a specific medical problem that is going to be corrected, maybe ... but usually not. I have heard of people who lose weight being able to get off the machine occasionally. However, unless there is something specific I don't know about your medical/apnea history, I think you might be in for lifelong cpap therapy

sorry...
feel free to PM me with any questions/concerns -- I got my machine a few months ago and went through all the trauma of getting used to the machine, etc.