Pros...
Nice text output, easy to read and good choice of colors.
Most common commands have shortcuts, eg. /b for /ban and /wi for /whois.
The script works pretty good and has a "solid" feel to it. Easy to chat with.
All of the commands are familiar, making the script easy to use from the start.
Very small download, under 75kb.

Features:
XDCC system for offering files publicly.
Text-based email checker.
Quote system for storing memorable quots.
Mass commands.
More basic features...

Cons...
Error-checking needs work, eg. "* /writeini: insufficient parameters (line 90, core.syn)" when a command is used incorrectly.
No support for different themes/colors. (the default colors do look decent, though)
No help system or full explanation for commands, although a full list of commands (along with syntax) is in the readme.
Minimal ways to get information about users or channels, eg. no clone/channel scan.

Conclusion...
This script is not going to appeal to everybody. For instance, it has no popups, dialogs, channel control, etc. This script is meant for one thing: chatting. Since there's a lot of people in which this type of script appeals to, I don't consider the lack of such features as a pro or a con. Some people never have the need for them. I do think that a theme system, even if to just change the colors, should be included.

Not really a con.. but should be mentioned. If you are a channel operator and are in a situation where you need to quickly op and deop certain people, eg. channel takeover, this script is not going to work very well, seeing as how you would have to manually type out all of the commands (there are mass commands, though.)

What I would like to see added:
Theme system.
Commands that react to selected nicks, eg /sdop would deop selected nicknames in the active channel.
Basic help which lists commands and syntaxes. For instance, if you use a command incorrectly, it could print the correct syntax.

Like I said, this script will not appeal to everyone. It's a matter of preference.