Here are some things about critiquing that I have found useful........
The first question in preparing a critique is to ask yourself what your intent is in offering the critique? Is it a gift to the builder? Are you trying to push someone to change? Are you trying to puff yourself up? Yeah... sometime we even need that..... can you admit that??
Second, share your opinion as just that, or the way you see it, or think it should be... Odds are you don't have the last word on the proper design and build of any rifle.... they seem to vary a lot............
Take into account the goal the builder had in mind as Rich said... bench copy, characteristic of a school, contemporary etc. Now you can describe things that match your notion of the ideal or that vary from your notion of the ideal.... notice I said describe..it takes work to paint word pictures....( how confident are you that your notion of the ideal closely reflects reality--do you have real first hand knowledge?). .... but if you really want to help the builder improve.... that is what it takes. Describe requires measurement and sensory grounded language..not judgmental abstraction..... This isn't the law.. its just what seems to work best if you want your feedback to be heard and valued by thoose receiving it..
You can also say what you personally like or don't like about the gun..its your opinion..just remember everyone is entitled to one... This is where the intangibles and aesthetics come in.... but even here, the more descriptive you can be...or by showing another gun for comparison, you can be more helpful.
If you don't know a lot about the type of gun being shown you can always say so and then express your appreciation or dislike
Where there is a problem most of the time is not the content of criticism, rather it is the style and attitude with which it is delivered.... useful feedback should help the builder....
So that my thoughts, hope they might be helpful to someone...... And hey...it OK to have fun...........
Besides that, I love this site because there is so much to learn and so many here who are so much further down the road than I.........