Whether it be due to a lack of knowledge or skill, there are a few things we couldn't get working. Honestly, it's mostly just a lack of 3D modeling skills.
It's worth noting that once you've read some of these things, you may never be able to "unsee" them. Move on if that sort of thing bothers you.

We wanted:

• High quality portal gun - We found a high quality portal gun model with great looking textures and more polygons. It was made for SFM and had a few differences from the model we're currently using that we couldn't fix.
  
• Fixed player model with legs - Due to Chell's and the Combine Grunt's armatures being different, I couldn't get the player model's legs correct.
  
• Pixelated portal view when getting too close - When getting too close to a portal, you might notice that it gets really pixelated. I created a toggleable post-processing effect to mask this, but it's still something we'd like to ultimately fix.

Maybe you can help!

If you're a 3D modeler and think you can fix these issues, feel free to post below. We might get in contact with you, and maybe you can (hopefully) resolve these problems.
As for the pixelated portals, that's more of a scripting issue. Again, let us know if you're a Lua/VScript programmer and would like to take a look. You could also decompile the addon files with Source 2 Viewer and take a look for yourself ;)