As you can see, Inbox is clean and minimalistic, with a Lollipop color scheme. After spending 15 minutes in Inbox, I can say it's not intuitive. You don't right from the start get how things work. It will take time to understand how inbox works and how you need to change the way you approach email to get the best experience from Inbox. First and foremost
"It would be best, if you have all your email in your inbox, instead of individual folders"
Inbox works best, when you haven' created any rules to auto archive emails to different folders. Now suppose you are one of the majority who haven't yet tried the smart labels in Gmail or created Extra folders to sort your emails, you are good to go.
You have Search, Hangouts shortcut & Google+ Notification Items on the Title bar.You also have a toggle, which shows the Inbox view and Pinned view.
With all the changes, the most confusing change is to the email item.
Email item when clicked, works just like a normal email. But Google wants your to treat your email as an to do item, marking them Done (which archives them) or postpone it for later, or pin it (so when you mark all done pinned items remain in the inbox). It seems Google is pushing you towards a clean Inbox.
Inbox carries the smart labels from Gmail and adds new smart categories and presents them as Bundles. New additions to the already existing (Social, Updates, Forums) are Travel, Purchases, Finance, Promos. You can also create your own bundles.
You can create your own bundles, which is just like the rules you created in Gmail. But with bundles, you have the option to surface the bundle either once a day or week when an email arrives. This leads to a lean & clean Inbox. Smart..
Folders are segregated based on rules governing them. If a folder has a rules moving emails to it it is shown as "Skip the Inbox", which you can convert to a bundle. If there is no rules but you manually move the emails the folder they are shown as "Unbundled". You can convert the "Skip the Inbox" folders into a bundle, while for the Unbundled ones, you still need to manually move them.
Reminders are a new addition to any inbox. When you create an reminder it gets added to your Inbox. You can do the same actions on it as on an email item. Mark it Done, Snooze it , Pin It or Delete it.
It gives you suggestions on what your type. As seen in the screenshot, i want to pay Airtel bill, if i just type "Pay Air" it starts giving me the topmost suggestions for paying bills. Which is helpful. You can also set a later date (which puts the reminder in snoozed section).
So these is what Inbox is right now, hope the article gave you enough insight into the new service. Please share it if you like it or wants your friends to find out what Inbox is.