Stayed here for a week for our first trip to Mexico. What a great, laid back place. It's easy to find, and is only four or five blocks from the beach, the main touristy strip (5th Avenue), and the bus terminal. It has a very friendly atmosphere; you get to know all the staff and many other residents, and there's always a friendly face. The room was always spotlessly clean, with refrigerator, TV, kitchenette, large bed, large bathroom, balcony with hammock, and a/c. The pool area is lovely.
Being a few blocks away from 'tourist central' is absolutely fantastic. You feel part of the town itself, and can explore some great restaurants (all much cheaper, better, and more authentic than down on 5th!) and food carts within a couple of blocks. If it's the 'real Mexico' that you've come for then you won't be disappointed.
If you'd prefer to cater for yourselves, there are numerous convenience stores nearby, as well as huge Walmart, Aki and Mega supermarkets just a few blocks away. The hotel is also very well placed for catching the colectivo (local minibus, ultra-cheap and fast) up and down the highway - the colectivo depot is only one block away.
Many thanks to the management and staff for making our stay so memorable. We'd recommend El Acuario to anyone!