What's great about Gmail Mobile 2.0? It works offline: you can preload messages from the inbox and from all your labels to read them when you are offline. You can also compose messages when you don't have an Internet connection and Gmail sends them when you are online.
The application notifies you when there is new mail in the inbox, so you don't have to constantly click on Refresh. It's now possible to save the credentials for more than one Gmail account and switch between the accounts directly from the menu. What's more, Gmail Mobile 2.0 supports Google Apps accounts, which previously required a separate application.
Some cool things to try:
* scroll using the left or the right key of your phone
* the updated interface for contacts which has more powerful search
To install the new version, go to m.google.com/mail from your mobile phone's browser. From what I noticed, this version is less responsive than Gmail Mobile 1.5 and it uses more data.