TRW, if you check back here ........
Comments can always be made in a positive sense about what you find you like in a painting .... colour, technique, feeling, tonal distribution, composition.
It's nice to start on a positive note
If something jarrs, try to pin it down to something like a shape or combination of shapes, do they sit well together, 'kiss' where they should overlap ... does the colour set your teeth on edge/
.... is the whole painting lacking in contrast of tone and /or colour/....... does the composition lead your eye around the work? ..... can you immediately find the focal point of the work, or it lacking?
These are just some pointers to help focus on a work and perhaps find something relevant.
If you really don't like a painting, don't post - that's the simplest solution