Opera Mini's start page now links to Google Search, Gmail and Google+. The search interface is very old and doesn't include the features released in the past 4-5 years. Gmail sends you to the basic mobile interface even if you're using a tablet. The Google+ web app is great and it works well in Opera Mini.
Obviously, Opera Mini is optimized for slow Internet connections and can't handle web apps properly because the rendering engine is in the cloud. Imagine having to reload Gmail every time you tap on a message, check your inbox or label a message.
While you can install Opera Mini on a smartphone, the browser is really popular on feature phones. "More than 168 million people used the Opera Mini browser in March, 117 billion pages were served and more than 19 petabytes of operator data were compressed for Opera Mini users," informs Opera. Back in November 2011, the top handsets that used Opera Mini were Nokia 5130 XpressMusic, Nokia 2700c, Nokia C3, followed by a lot of other Nokia feature phones and Symbian phones.