Editors' note, October 24, 2014: This review was updated with information about the latest version.
Keynote (iOS|Mac) is Apple's presentation software which lets you choose a template, create and edit slides, add animations and transitions, and has numerous charts, tables, and graphs to get your message across. And now, with iOS 8.1 and Yosemite, you can use continuity features to hand off your work between devices.
Keynote was built from the ground up for both iOS and Mac, and just like the other iWork apps, the iOS version continues to improve, while the Mac version is still playing catchup from when Apple gave the apps feature parity across devices. Due to a backlash of user complaints about the Mac versions, Apple has since added more features, but it still isn't on par with what you had in iWork '09.
Before I start, know that I did most of my testing on the iPad. You can get Keynote for your iPhone (just like the rest of the iWork apps), but the smaller screen makes it much harder to create and edit presentations unless you're using an iPhone 6 Plus. You don't lose functionality when moving from the iPad to the iPhone, and it will come in handy in a pinch, but using it on the iPad is a much better experience.
Navigating the interface
You can navigate from slide to slide on the left side of the screen, with the current slide in the main viewing area. On top are buttons for editing objects in your slides, adding new objects such as photos, graphs, or shapes, along with other tools and sharing options. In the bottom right, a plus-sign button lets you add new slides to your presentation.
Creating a presentation
To get started, you can choose from 30 themes that give your presentation different looks for everything from information-heavy bulleted lists to photo- or graphics-focused shows. Once you choose a look you like, each theme comes with several pre-made slides that fit with the overall aesthetic while letting you double tap on placeholders to add your own images and text. The new Keynote comes with almost twice as many themes than you had in the pre-iOS 7 version, and while you lose some animations and transitions you had before, the new version adds new ones that look great.
Like any good presentation software, Keynote gives you the ability to create eye-catching motion with objects in your slides through animations and transitions. You can touch an object, such as a block of text or an image, then select the Animate button from the pop-up menu. A new set of buttons then pops up where you can select build-in (the animation that occurs when you first touch the screen) or build-out (another animation when you touch again) animations. There are 24 animations to choose from and all produce a great looking effect.
When you want to transition between slides, you can touch a slide in the left navigation area and then select Transition from the resulting pop-up menu. There are 30 transitions to choose from including a few new ones in the latest version of Keynote. But there's another transition option called Magic Move that's a neat way to keep your audience focused on your message.
Magic Move uses an object or image in one slide, then does a zoom animation to the position of the same object or image on the next slide. So if you have a slide with an image of a toy car at the top of slide A, and the same toy car shows up in a collection of other toys at the bottom of slide B, you can use the Magic Move to keep the audience focused on that toy car as it transitions to slide B. It's hard to explain, but it's a neat effect to add to your presentations.
Other useful features
The iOS version of Keynote lost a couple of features in the overhaul to get feature parity across all devices after the rollout of iOS 7, but it also received some new ones.
Interactive charts let you start by creating a regular chart on a slide and then lets you include how the data changes over time. During your presentation, you can show the gradual changes in your data by using a slider. To round out the experience, you can add a background track to your presentation from your song library.
The app also lets you make all or a part of an image transparent using a tool called Instant Alpha, a feature borrowed from the older Mac version, that gives your slides an even more professional look.
Collaboration and iCloud Drive
With all three iWork apps, you can invite up to 20 people to work on the same document simultaneously and you'll see other users interacting with the document in real time. The app color codes each user so you know who is working on a particular section. People also can make comments on sections that show up for all people sharing the document. These are things that Google Docs already does, but it works great on Apple devices as well.