Cost: FREE!

Pros and Cons:

Initially it is not just as simple to use as the web client or other clients you were already familiar with
There is not a huge amount of readily install-able add-ons available for Genesis... yet..
It is a little bit complicated to take stuff created by others and tweak it how you'd like

List of Packages You Can Install for Gen:

Compiling the packages for mudlet that people in the Genesis community have shared for others to be able to add them.

Mudlet Package - Magic Map Magic Map Package by Findis, from forum here
Mudlet Package - Magic Map Windowed Findis's magic map package with Dakhor's tweak to make it windowed applied, from forum here
Mudlet Package - Vitals Vitals Package by Dixel, from forum here
Mudlet Package - Mudlet Mapper Config Mapper config which you have to install to start creating your own mudlet maps of the mud. Shared by Dixel on forum here
Mudlet Package - Numpad Direction Keys simple set of action keys to help moving around
Mudlet Package - Colour Exits striking colours for the exits
Mudlet Package - Chat Window adds a chat window that captures messages!
Mudlet Package - Combat Colours adds colour triggers for regular damage hits in combat
Mudlet Package - Command Queue a simple way to set a delay for sending commands to the mud

Dixel's set up posted on the Gen Forums. Can see that they have magic map as well as a nice status panel

Dakhor's Setup also from the Forum. Can see they have the magic map windowed and also are using mudlets own mapper. They have status bars and a tabbed chat window.

Inspiring Examples from Other Muds:

Really nice GUI for status bars, found on Mudlet Forum here
Example of Totally Tweaked GUI with the MUD window in the middle, found by google image searching mudlet

Example of just having a nice artistic image to keep you company lol, found by google image searching mudlet

Example of EXTREME customisation where the game ends up looking like Zelda or something! found by google image searching mudlet