First, a word about my bona fides: I lived in Argentina for two years and I have visited Iguazu Falls seven times since 1976.

When planning a trip to the Falls the importance of hotel location cannot be overstated. You really, REALLY want to be within easy walking distance, so that 1) you can conveniently visit the Falls at different times of the day; 2) you don't have to hassle with the taxi-to-the-bus-to-the-shuttle-to-the-train (or so it seems) transportation headache to get there from town; 3) you can conveniently time your Falls visits to avoid the worst heat and crowds, and 4) you have access to the Falls (if you are sufficiently enterprising) at the best possible time: in the early morning before the park officially opens (more about this later). This hotel is not just a five-minute walk from the Falls -- it is the also the only hotel on the Argentine side within 10 kms of the park. If you can afford it, or even if it strains your trip budget, spend the extra money and stay here -- don't give it a second thought.

As for the hotel itself: Above-average, recently renovated rooms; first-rate breakfast buffet;
very decent (if expensive) restaurant for lunch and dinner; affordable spa and spacious workout area with a good selection of equipment; pleasant pool area; helpful staff. But I have stayed at this same hotel in years past (including before it was owned by Sheraton) when NONE of the above were true, and I would still have recommended it because of its unique access to the Falls.

As for entering the Falls viewing area before the park opens: This can be done. From 5 PM until 8 AM there is a "No Pasar" saw-horse blocking the path from the hotel to the park, but we entered and walked around the Falls both before 8 and after 5 and never had a problem.
(Years ago hotel guests could always go in and out of the Falls viewing areas whenever they pleased without restriction, so we got accustomed to these early morning/late afternoon visits.) We ran into a few maintenance workers with leaf blowers, etc., but we smiled and waved and they smiled and waved back -- that was it. 6 AM is when you'll see the Falls at their best, and when you're most likely to see wildlife. And you'll have the place to yourself. Caveat: I can't guarantee that some over-zealous bureaucrat won't come out from behind a bush and give you grief, but the worst that will happen (unless I completely miss my guess) is that you'll be informed of the rules and shown the way to the exit.

A couple of more tips:

1) Get over to the Isla San Martin without fail. The views of the falls from the island are the best in the park The only way there is by a small boat (no charge) that does the crossing in about 90 seconds and starts running at 10 AM. The line of people waiting will quickly get long (and unbearably hot -- very little shade down there), so get there by 9:30.

2) Skip the expensive commercial boat rides that go up and down the river, near the base of the Falls, etc. Your views are just as good from the park trails, and, trust me, you don't want to be wearing one of those canvas life vests after 37 other people have been wearing the same one in the 97-degree heat.

3) Only go to the Brazilian side if you have extra time. The Argentine side is more worthwhile. If you're a US citizen, don't bother, as they will charge you $120 for a visa even for a short visit (We have our own dumb state dept to thank for this nuisance -- Brazil is paying us back for our own obnoxious and unfriendly treatment of Brazilians who wish to visit the US.)

4) The Sheraton has a traveler-friendly (and, alas, increasingly less common) cancellation policy -- no penalty 72 hours prior to check-in. Book early, and then check back from time to time to see if the rate has fallen -- it's easy to cancel and rebook at the lower rate. We saved $280 on our 2-night stay by re-booking a week before our stay.

5) Rooms with a view of the Falls are maybe $50 extra per night. Worth it? Hmmm. If you can get the top floor, maybe so. But we always book the cheaper, non-view rooms and use the money saved for a nice dinner. It's your call -- you won't go far wrong either way.