Thanks a lot for the constructive feedback! This is all very useful information and I will definetely follow your suggestions. I agree with you that the decklist UI is not the best and I should improve the whole UI. The tool is derived from a stand-alone version of another tool I was using to create cards for myself so it still suffers from a bit of programmer-oriented design.
My idea is to have the card preview look more than the actual card, with an HD preview popping up like a tooltip when hovering with a mouse. Right click for adding cards seems better as well.
Can you attach a screenshot of the "compressed text" you mentioned so I can investigate further? Also, what monitor/window resolution are you using? Are you on windows or linux?