We spent 24 days on the Diamond Princess, two back-to-back cruises. The quality was Princess standard, very good but not exceptional. My comments will focus on what we did rather than the ship's features.
First, the cabin. We had E633, an obstructed view on Deck 8. It's a good cabin. The window is between two lifeboats, so the view is relatively unobstructed. The cabin door is right across from a stairwell, which worried me at first, but the incoming noise was minimal. There was no noise coming from the Promenade Deck below (other than occasional loud walkers). We liked it a lot. It was convenient to the Promenade Deck (we like to sit and watch the ocean go by) and to everything else.
As platinum members, we appreciated the fact that the Skywalker Lounge was often reserved for us. It was a great place to read, and the evening drinks before dinner were pleasant. However, sometimes they had it closed for private functions, somewhat disappointing.
We had two visits to each port, and had been to them all before. We almost always arrange our own days ashore, avoiding the ship's tours. I'll ignore Sydney and Auckland, splendid cities, since most cruisers spend several days in one or both cities before or after.
Melbourne is a pleasant city. The city staff will sell you a transit pass upon leaving the ship. It's all you really need. The city can easily fill the day. Great shopping. We like the (free) art museum. We also took the train (covered by the transit pass) out to Willamstown, a pleasant town with great coastal walks. If you're a naval fan, there is a WWII era corvette one can wander about for a modest fee, staffed by old salts.
Hobart: We like Hobart. Again, there is enough to occupy one in town. One of our visits, however, we rented a car. Now, for Americans, Tasmania is a great place to risk Australian roads. Hobart is a modest-sized town, and once out of town in any direction the roads are relatively empty and the scenery great. We drove through the Huon Valley, but have in the past been out to Richmond. There are vineyards, great beaches, and all sorts of interesting stops. Can't go wrong.
Port Chalmers/Dunedin: Our first visit, the weather was wretched. We simply wandered around (in the rain) Port Chalmers. There is a scenic path along the coast, easily done on two hours or less, and even in the rain it was good. The second visit we rented a car and drove north. There are some great beaches, long, wide, and empty. And hardly any traffic. If you really want to take the train, you can usually book a spot just after getting off the ship. Dunedin itself is a pleasant town to walk about.
Akaroa: Since the cruise facilities at Lyttleton (for Christchurch) won't be repaired until about 2017, Akaroa is the alternate stop. It's a village, with no rental cars available. If you want there is a bus available on shore that will get to back and forth to Christchurch. We did something quite delightful: the Akaroa mail run. You'll find it with a web search. The local postie takes up to nine passengers in his mail run around the Banks Peninsula, with running commentary on all sorts of things. There are regular breaks and a pleasant snack. The only risk is that if the ship isn't able to tender in, you don't get a refund (and our second visit was cancelled due weather). Still, worth the risk and I'd strongly recommend it.
Tauranga: An easy port to do-it-yourself. The first visit, we rented a car (advance is good, but you can usually get a car upon getting off the ship). We drove up and down the coast. On a previous visit, we spent the day in the Rotorua area. Again, driving in New Zealand is no problem given the limited traffic. The second visit, we stayed in the port area. There is a great walk up the nearby volcanic cone. Spectacular views, and quite enough to occupy three hours. The beaches in the area are also spectacular. It's an NZ beach town, with lots of shops.