Hi there,
On the surface they do look similar, they are both calendar apps after all.
However myCal2: eventium has some major improvements over myCal 1. Off the top of my head:
- Much faster loading (especially on newer devices)
 - New year view on iPad devices with full AirPrint support. Events can word wrap and each month within the view is vertically scrollable
 - Revised month view, includes multi line word wrapped display (configurable number of lines) of events, and vertical scrolling of each week within the row
 - Revised, day, week and list views
 - Can now mark editable events as complete with a custom colored tick or strikethrough
 - Event long tap menu is context sensitive, so invitees can be contacted directly (if any), and can create new events from contact dates  (for anniversaries and such)
 - Day long tap menu improved and is also context sensitive
 - AirPrint print preview is now supported
 - Cleaner look and feel
 - Better invitee support
 - Better timezone support, can now see the timezone on the event itself if you aren't in that zone, for example
 - Can set day background color and image, and can copy the color and/or image to other days
 - Improved alerts and repeat rules
 
Pretty much everything has been improved over the existing myCal 1 functionality.
Regards
John
EDIT: Updated with a few more enhancements