I've been trying out Feed Wrangler over the last 12 hours or so, and I'm mostly loving it so far, but I agree with the general consensus that the web interface isn't the prettiest thing around. Now, this is totally understandable since it was more important for David Smith to get the thing off the ground first, but it doesn't change the fact that the UI could use a little polish.
Thankfully, Preshit Deorukhkar – the lovely man who runs the Beautiful Pixels blog – has come up with some nifty tools for improving the overall look of the UI. The first is a Safari extension called Feed Rango, and the other is merely a set of CSS rules to accomplish the same task. Personally, I'm using the CSS rules in a Chrome extension called Stylish.
[Update: Feed Rango is now available as a Chrome extension. I'll be switching to that from the CSS rules shortly.]
I'm sure that Feed Wrangler will inevitably get a redesign at some point, but my thanks goes to Preshit for making the current experience a lot more enjoyable.