One engine to rule them all
Right off the bat, HeroEngine united all aspects of game development under one roof. You have the tools for the artists, world builders, scripters, and even management all packed into the same suite. Your artists have all the tools that they need to do texturing inside of the world, even while world builders are using said textures in their map creations. Scripters can stay on the same page with a script management tool, and management can oversee the whole process by whiteboarding directly on top of the game and using other management tools to keep track of what everyone is doing.
Remote collaboration and simultaneous development
Probably the biggest feature of them all, however, is that developers work within the game's client directly. They connect to the central server and log into the game world to create whatever they need to create. The entire team logs in this way, letting them collaboratively work on regions of the world and letting them see all the changes in real time.
Developers have said that it feels like playing an MMO while building an MMO. Developers can take control of characters and actually move around the world in the exact way a player would, letting them experience the game first hand without inserting any guesswork. A developer can even switch between developer mode and client mode at will, so they can play what they've just created to check for bugs right on the spot.
Also, because everyone is logging into the main server, this doesn't require your entire team to be local to an area. The team could be in Texas while you're in Maine, and you can still gain access to all of the tools that you need to use to work, and still work with the rest of the team collaboratively in real time.
So instead of working on multiple tools, bringing all the work together and merging it into a release client for testing, you just flip back and forth between game and development as you wish, while the guy from Maine and the guy from Florida continue working next to you.
What if I like those other programs?
HeroEngine is also built around ease of use. If other team members like using Photoshop or 3D Studio Max, it's actually not a problem. Those members can still create assets and and then drop them into the system, which makes the asset now immediately available for everyone else in HeroEngine.
If the assets need updating, you can go in and update them and they'll all immediately update in the environment for everyone to see. Basically, all of this streamlines the production process and eliminates downtimes and having the need to constantly re-edit work.
Plus, if HeroEngine doesn't come with what you need it to do, the system can be easily customized by the team using it. The best example of this is BioWare, who has completely modified HeroEngine to fit their needs for the upcoming Star Wars MMO.
All in all, HeroEngine is an amazing tool that is going to streamline development processes while simultaneously allowing developers to create fantastic games. This means better games made faster, and who doesn't like hearing that?