This is a really good system for forum article and layout management. It offers functionality that other plugins just don't match.
The article/feature system offers a great way to highlight content in visually appealing wrappers. It can be a bit confusing to use at times as there are a lot of controls, but the controls are good.
The layout management is robust. It would be nice to have some more customization of positioning, but for what it offers, as visually as it does, this is amazing. No other plugin matches how easy this is to use, with this flexibility. That being said, it would be even more awesome if the configuration were streamlined a bit more - but as it is, it offers a lot of functions.
Some of the styles may appear a little strange with some XenForo themes. It would be nice to see a style properties panel added to the XenForo admin cp. For example, on my forum there is a difference with hyperlink styling in messages and the color palette styling, but XenPorta only recognizes the palette styling.
I'm sure people who could code, or are very familiar with CSS can go beyond what XenPorta can offer. But for those who are not, or who are looking for something useable, stable, robust, and flexible, XenPorta is it.
The last thing I would as for, is better written documentation. There are several videos on YouTube by jax (which are not even linked here), but written documentation would go a long way too. -- that gives me an idea, maybe i'll try to help write stuff up.