In Puget Sound itself the water is fairly cold year round, high 30s to low 50s is about the max range I've seen. The water is green with a great deal of particulate suspended in it. Vis can be pretty good, especially at depth if you do a lot of shore diving, but you may have to get below a layer of 'bloom' before it clears up. In my experience the water seems much darker than east coast diving, its tough to have "too much light" for diving in Puget Sound. (I often wish my Helios 9 18 watt HID was twice as bright...)
The tidal changes ensure that a great deal of water moves into and out of the sound each day, keeping things stirred up. On the other hand, this leads to a lot of bio-diversity, and swimming with seals, large jellyfish, giant pacific octopi, and a wide variety of fish and shellfish keeps life interesting. There are no lobsters (darn), but there are scallops and a huge assortment of nudi's and other small life forms available to macro photographers on many dives.
The tides can be dangerous, ignorance can be fatal. Several divers have been killed or injured each year for the last several years by misjudging or paying insufficient attention to the tides.
With good planning and good thermal protection, however, diving in Puget Sound is very enjoyable and it offers a broad range of dives from entry level to highly technical.
Here is a really nice website that offers lots of additional information about diving in both Puget Sound as well as points north:
http://staff.washington.edu/parker/scuba/index.html