I have received my welcome email from Pottermore the day before yesterday and I would like to tell you how I like it so far.
Exploring the Chapters
This is in my opinion the main thing you can do on Pottermore and I really liked it. The pictures for the different moments are very beautiful and I love the fact that you can zoom to three different levels so that different things come into focus. This makes everything seem more real. When you move the cursor to the left or to the right, things in the picture that are closer to you will move further on the screen than things that are farther away. This gives a nice sense of three-dimensionality, although you can't move sideways very far.
Some objects will show a reaction if you cross them with the cursor, which makes exploring more exciting and shows a love for detail. Collecting things also makes it more interesting, although you can't really do anything with most of the objects, but at least you receive house points.
I can gladly say that the site exceeded my expectations optically. However, I think the moments could be improved if you could find something on every zoom level of every picture to make the zoom function more sensible, but in most moments you really can't find everything without zooming, so it is quite good already.
But now about the content: In each chapter you can read about the characters, objects, places etc. that appear in this chapter in the book. Most of the content is headed with "From the Story", which means that you already know what they tell you there if you have read the book and I skipped most of those (in general very short) texts. However, there are also parts headed with "New from J.K. Rowling" (which means new background information for the story) or "J.K. Rowling's thoughts" (e.g. why she chose certain names for certain characters). I found those texts very interesting to read and especially enjoyed Minerva's story. You can find information on her life in three different chapters so you get an agreeable amount of text.
Buying Your Wand and Getting Sorted
These were two of the features I was especially excited about and I enjoyed answering the questions. Sometimes I had to think really hard to decide for one option, so it took me quite a while. I like the fact that you do these two quizzes at the right time in the story, so you won't belong to any house until the Sorting Hat chapter. A small negative result of this is that you only get points for collecting stuff from this point on, so people who find certain objects only when they go through the chapters for the second time (when they have already been sorted) will have more house points in the end that those who found everything at once.
As for the Sorting Hat - I still think that you can know better which house suits you best yourself than the website could know from the seven questions you answered. I would like it better if everyone had to answer a greater amount of questions from J.K. Rowling's pool. Of course, 7 is an important number in the books, but I would value a good Sorting result more than this symbolic aspect.
I found most of the questions very interesting, but I didn't like the question "Black or white?". Are you supposed to choose the colour you like better (e.g. what you prefer to wear) or should you consider the symbolic aspects? I've got the feeling that this kind of questions rather tends to distort the result than help finding the right house for someone.
Potion Brewing and Dueling
Once you have explored all the chapters, this is what remains for you to do until the next book is published. Like this you can earn more house points, however you might also lose some if your Potions explode. If you fail to brew your Potion correctly, but it doesn't explode (which hasn't happened to me so far), you will get one point for trying. Personally, I think the difficulty is appropriate because it would be kind of boring if you succeeded every time. I also think it is really helpful that you can practice the "Cure for Boils" without using up your ingredients (which you have to buy in Diagon Alley - but you have got lots of money!) and without risking to lose points. However, I wish you could also practice the other Potions before actually brewing them because it is much easier if you already know what to do without checking the book after every step because there is a time limit.
The time you have to let the Potion brew before you can do the last steps can be a little annoying (the Cure for Boils for instance takes 1-3 hours depending on which cauldron you use). On the other hand, it also makes the experience closer to reality.
Just as the Potions, you can also practice the spells before you actually start a duel. This is really necessary because I think that the explanation how to do it is not very good. At first I didn't know that you have to click each letter twice (not only the first one), once when the line hits it and once when the ring reaches its highest radius.
I like the fact that different spells have different difficulties and the harder ones will lead to better results.
At the moment, dueling is undergoing maintenance, so I couldn't try out my skills against other users yet, but I already know that you can only earn house points if you win against someone from another house. This is quite a good thing because otherwise people would just keep dueling their house mates so that your house would get points no matter who wins.
What needs to be improved most on Pottermore in my opinion is the interaction between users. I really miss the option to send someone a message.
If you add someone as a friend and (s)he adds you back, you are able to see his/her profile and which chapter (s)he is currently exploring. However there isn't much more to it. The only way you can "talk" to other users is by leaving a comment in the Great Hall (where everyone can see it) or in your Common Room (where only people from your own house can see it).
How the Site Is Working So Far
On my computer at least, Pottermore runs quite well. At some points, collecting an item didn't work at the first try, but that didn't happen very often and I always managed to collect it in the end, so it didn't annoy me very much. Once I had to wait for a while before I could continue exploring because they were just doing some updates, but it's obvious that this can happen in the beta phase. What I was really glad about is that most of the time there weren't any long loading times. The only thing that sometimes took a moment was adding an object to my trunk.
In the corner of the page there is a button for giving Pottermore feedback. If you press it, a poll will open up. However it is a very short one and I wonder how they can take much out of it. I didn't find any space were you can make a concrete suggestion how the site could be improved. Of course, you can tell that in the comments below chapters, but I don't think they read all the comments because there are just too many and some of them just say things like "I love Hermione so much".