Features in and of themselves are a very poor way to judge an application since they tell you nothing about the user experience, or how intuitively or intelligently it is designed. Features don't reveal anything about the quality of the code, or the performance, or the attention to detail, or security practices. The only way to really judge an app is to try it and get to know the code. Installing CodeIgniter is child's play so we encourage you to do just that. In the mean time here's a list of CodeIgniter's main features.
Model-View-Controller Based System
Extremely Light Weight
Full Featured database classes with support for several platforms.
Active Record Database Support
Form and Data Validation
Security and XSS Filtering
Email Sending Class. Supports Attachments, HTML/Text email, multiple protocols (sendmail, SMTP, and Mail) and more.
Image Manipulation Library (cropping, resizing, rotating, etc.). Supports GD, ImageMagick, and NetPBM
File Uploading Class
Full Page Caching
User Agent Class
Zip Encoding Class
Template Engine Class
Unit Testing Class
Search-engine Friendly URLs
Flexible URI Routing
Support for Hooks and Class Extensions
Large library of "helper" functions