I will start off by saying that I got this on Priceline for under half of what they were asking for the weekend I was there. So that colors my image a bit - all hotels were ridiculously expensive that weekend and I probably wouldn't have been happy with any for the asking rate! We stayed here for two nights before a cruise. We stayed at the Hyatt the night after the cruise and I'll write a review for that as well. (Which would I choose? They both had good and bad - I'd take whichever gave me a better deal but I thought the Hyatt had a bad pool/fitness room but a better location.)
That said, getting there was easy - about $25 cab from the airport. The room was nice - we had a small balcony that overlooked the bay and the Doubletree pool area next door. Two chairs and a small table - I doubt more than two people would be comfortable out there, though - it was tiny! The room was decent sized, had a nice closet and an OK bathroom/sink area. Toiletries (shampoo, conditioner, soap and lotion) were by Bath and Body Works. There was not a fridge in the room. And no full-length mirror - what's with that??? It was the same at the Hyatt!
There was a small "mall" between the two hotels (Marriott and Doubletree) where you could get something to eat and there were a few shops there. The hotel lounge was nice and the service was good but of course it was very expensive as with any hotel food. (Tip - the food was the same price in the lounge as it was from room service, though you probably had to pay a delivery and/or service fee for room service. But it you really prefer room service it's probably worth it. We figured the prices would be a bit cheaper downstairs but they were not.) Tip about Miami in general that I read specifically about South Beach - some (most?) restaurants will add gratuity to the bill right away - so check that before you decide how much to tip! The lounge didn't do this but we ate at Tradewinds at Bayside and they did add 15% to the bill.
We did not use the pool but we could see it from our room and walked down there one day. It was OK but the pool at the Doubletree looked nicer. There was also a hottub and they had a ping pong table set up down there. It was a nice big area so if you wanted to just lay in the sun or shade there were plenty of areas to do so. You could also get down to the waterfront easily from the lobby area and it was nice to stroll along the sidewalk along the water - there are lots of boats at the marina right there.
The fitness room was quite good - several weight machines (sorry - don't belong to a gym so I can't say if they were diverse enough but they looked pretty new) and several treadmills, ellipticals and bikes. They all had a TV but I found the sound and TV to be hit or miss on them. One I couldn't turn the channel and another I couldn't get any sound. The other one I used had sound SOMETIMES so if being entertained while running/elliptical/biking is important, bring your I-pod - they all had a connection for that. They did have headphones available in the fitness center for the machines, which was nice. The best thing about the fitness room is that you could easily see the cruise port from the room. Nice view!
The hotel is not really near much as far as walking distance but the metromover is just at the end of the street (not even a full block) and it's free so it was very easy to get to Bayside Market where they have stores and lots of restaurants. It was a really fun place. Getting back was far more difficult for us as we kept thinking we were going the wrong way and we'd get off, examine the maps, get on the next train and find the same problem again. I'm sure someone more experienced in public transportation would fare better. (We did finally get back but we switched trains several times!) The people on the metromover were OK but I wouldn't ride it alone (as a woman) and I would either be back to the hotel before dark (the area around the hotel was OK but it wasn't super well-lit and there were few people around) or take a cab - I imagine it's not more than $10 from Bayside. We did the Island Queen boat tour at Bayside (there are lots of boat tours and I imagine they're all about the same). They leave often so you should be able to find one that suits your timeframe. Island Queen also had a lot of other tours with discounts if you paired things (i.e. boat tour and a hop-on-hop-off city tour, Everglades tour, etc.)
We took a taxi to the cruise port, which was $9.30 before tip and took only 10 minutes or so. Pretty easy. We tried to do self-checkout on the TV before we left but when I checked the bill I found that they'd charged us for one night of parking (over $20 but I don't recall how much) so we had to go to the desk to get that charge removed. They were very friendly and easy to deal with both at check in and check out.
I would definitely stay here again - if you really want to be close to action, I'd choose either something closer to Bayside or someone in South Beach but this was perfect for two nights and essentially one day in Miami before a cruise.