Snooker players value "even" chevrons on their ash cues. Chevrons are the arrow-like grains on the shaft. If the chevrons are well formed and evenly spaced on an ash blank, it's likely to be used for more expensive cues. There should not be too many, or too few. Also the straight grains should run straight up and down the shaft. (These are found on the opposite side from the chevrons). These things are perhaps the most "exotic" features of a snooker cue, to someone who's used to pool cues. The chevron thing is mostly about aestetics, I think, but obviously straight grains are always a plus.
Other than that, the balance, the hit and of course wether real exotic woods are used are important indicators to the quality of a snooker cue. The cueaper snooker cues are mostly using ebonized wood rather than proper ebony for the butt and are heavily artificially weighted to compensate. The cheap cues that use poor quality ash have very dull hits. When you compare with for instance a Parris cue or any other quality maker, you'll notice the better cue being much more springy and responsive.
The picture shows what I'd consider a good amount/spacing of chevrons in a shaft, though they can always be more well formed, and again, the straight grains are the most important thing.
Then there are such things as machine- vs. hand splicing of the butt, or wether the butt is properly spliced at all. Some cheap cues have a metal decorative "band" around the butt where the cue is glued and threaded, rather than spliced. Mye friend had one of those, I think it was a BCE "Ronnie O'Sullivan" cue. He sanded it and found out that not only was the butt not properly spliced but it was only superficially painted black. Those cues are not good!
