I've been a member for a little over a year. While I like a lot of Melia's hotels, their reservations system, their website, and the MAS program are almost useless.
On 3 out of 5 stays (all booked on the Sol Melia website at least 24 hours before arrival), the hotel had no record of my reservation when I showed up. Their staff who answer calls to the North American 800 number don't seem to be able to retrieve reservations booked through their website, and frequently claim that hotels that show availability online are sold out. I have found that the only way to change a booking is to cancel it on the website and rebook it on the website.
Lastly, my MAS points haven't even once been posted until I have submitted missing stay requests. Not impressive.