we flew with them last summer. They codeshare with KLM, so you can either be on a KLM plane or a Northwest.
I've just been looking on KLM's website, and they are showing it slightly cheaper, I think £321+tax, take a look on the left side where it says specials, and then look at Action Fares, these appear periodically and can be extremely low, we paid £185+tax last year but I think that was the 9/11 effect.
see
http://www.klmuk.com
We flew KLM to Amsterdam, and then Northwest to Miami, KLM are a great airline, I have no complaints about them at all. I can't really complain about Northwest either, they did nothing wrong, but the plane felt quite old and a little shabby, It just wasn't anything special. They have no seatback tvs, but had movie screens at the front, the food was fine, leg-room ok - like I said, no specific complaint.
One thing I would check, is that I didn't think they flew direct to MCO, I thought they flew direct to Miami and Tampa and that flights to MCO were via either Miami or Detroit, this maybe because when we tried to go last November it was low season, I'm not sure, but we couldn't get a direct flight at that time (Direct from Amsterdam I mean, you will have to change in Amsterdam regardless, but that is not a big deal).
If you can't fly direct to MCO, I would look at Tampa, it's only an hours drive from Orlando and is supposed to be very easy. We flew to Miami last year, and it was fine, but it is a longer drive.
I would have no hesitation flying KLM/Northwest again, particularly as they fly from Regional airports and changing in Amsterdam is really quite painless. I'd rather do that than change at Heathrow anyday.
Bev