For example:
I really like the heatmap but I think some improvements are possible there.
I'm still missing gpu support and Zen should also think when his opponent must play a move.

What I like: it's the strongest commercially available program and it looks better than its competitors, IMO.

I don't like that it stops analysing after a few minutes. It should analyse as long as the user wants. And why is the longest time setting only 120 sec/move?

There seems to be a bug somewhere. If I investigate alternative moves while the program is analysing it freezes sometimes.

I would like an easy to use interface so that I can let Zen play against other programs.

A display of the main line and the possibility to let Zen analyse while the opponent is thinking would also be nice to have.

It would be more convenient if we could buy the program from Steam. The website, where we can buy it now, is half English, half Japanese, which might deter potential customers from buying it.

Zen is relativly expensive. A discount for customers of the previous version would be welcome.

I really like Zenith Go 6.

strong AI
clean user interface
good game review tool (Analyze function and moving through game with mouse wheel)
nice graphics (I would like to be able to turn off the small black border around the white stones)
fast startup
you can run two instances (to memorize pro games for example)
manual replay function (memorize pro games)
good sgf editor
fast startup
rated games
best of seven games
tsumego (300 problems)
voice over
cho chikun

Some things that could be improved:
add a tree view
option to move through game just with the cursor keys
improve movement through different variations

Zen is not only a good engine but also a very good go program.

My #1 dislike about Zenith Go:

• No Mac version

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UI is really not that good. There is no visible game tree like in Cgoban and the alternative moves controls are not intuitive at all.
It just brings a lot of frustration when you try to analyze your games.

Second this