Can light floods are not that uncommon. From your post, it is unclear to me whether the head or the can flooded. If it is the canister that flooded (assuming that by brand name, you meant Halcyon, Dive Rite or Salvo), it was most likely operator error. The o-ring must be installed and clean - a single hair on it can be enough to cause water to get into the can - and both latches need to be latched at the same time to be sure that the o-ring seats properly. If it was another brand that does not seal with an o-ring and two latches (like Sartek, OMS or Greenforce), I can't comment. In any case, take it back to the shop where you bought it and have them check it.
If the head flooded, take it back to the shop where you bought it and they should take care of it for you. It is definitely a defect.
The amount and quality of light provided by HID canister lights is more than worth the trouble.
Just to clarify, all Green Force batteries are sealed and can't leak, we do not use locking latches.
Thanks - Greg