Location: The garage is pretty easy to find. It's located about a mile north of the port. The operators of the garage put out a sign near the entrance that says "cruise parking" so there's no confusion as to where you should park (there are other garages nearby).
Facility: The garage is built like a tank. One way in/out and it is locked with an iron gate after 7:00 PM every night. I had NO reservations about leaving my car there. It is a standard multi-floor parking garage with overflow on the roof.
Service: Who cares about service? It's a garage, right? Well, here was my experience. There is a man standing right inside the entrance who checks your paperwork, pulls the ticket from the machine and tells you which floor to park on. Once you drive up to the cruise parking levels (I think the lower levels are used for hourly parking during the day) the shuttle driver is standing by to direct you into a spot. It's important to point out that this is NOT a valet lot so you don't have to worry about the staff having a bit of a "Ferris Bueller" with your car! The shuttle driver pulled the shuttle van right up behind our car so we just pulled the luggage out of our trunk and he loaded it up in the van.
Shuttle: The main advantage of this lot is that the free shuttle is round trip. All of the other long-term lots I could find in the area are over by the airport. Most don't provide a free shuttle at all, and many only provide shuttle service to the port, leaving you to take a cab back from the port to get your car. The shuttle dropped us off right in front of the terminal for our ship and handed our luggage off to the porters.
The return trip was painless as well. As we walked out of the cruise terminal we spotted the shuttle loading up some passengers and leaving. We only had to wait about 10-15 min before another shuttle from our garage came by and we flagged him down. The bags were loaded up and we picked up a few extra passengers from other terminals and we were on our way back to the garage. Overall a VERY painless procedure. Since I pre-paid for the parking I simply showed the man at the entrance/exit (same one from a week before, probably the owner/manager) my paperwork and was on my way.
In summary I can strongly recommend this garage as an excellent alternative to the $20/day garage at the port. Almost half the price and just as convenient IMO. Of course, this was just my experience... the lot was pretty full so maybe we'll get some more reviews.
Sorry for the long-winded review but I hope it is helpful for others as alternative parking for the Port of Miami seems to be a fairly regular topic posted here
Edit: I forgot one big disclaimer. The vans used for the shuttles said "CBM" on the side. Now, the lot was in no way identified as a CBM lot and is NOT the infamous CBM lot over by the airport that so many people have complained about. I read the reviews on that site and most of the problems were related to damage done to the cars or something similar. I attribute that to the the lot being valet while the lot I used was self-park. I don't know if this lot has anything to do with the "other" CBM lot, but my experience was quite positive.