Just last week Dungeon Defenders v3.0 was submitted to the Apple App Store for approval and the Android version would be released upon approval. However, this didn't pan out and V3.0 was not approved - so we get v4.0 along with a new array of features.
The exact details are being kept quiet until the application is approved, but Trendy Entertainment's Jeremy Stieglitz did mention a few changes on the company's website. First off, everything that was set to launch in v3.0 will launch in addition to the changes in v4.0.
The game will be updated with new levels, game modes and even a new shopkeeper. Speculation includes that pets will be available for purchase via mana from the new shopkeeper. As for the new game modes, we know one of which is titled "Competitive Mode," but details to what it entails are quiet at this time.
Expect the update hitting the Android Market here in the next week or so, along with an official changelog.