Blueberry makes an excellent mead, but if you're using whole fruit you have to be very aware of when to pull the berries as they are very tannic. It goes through the whole range of red wines (from lightly tannic port, to heavily tannic shirah/zin) in about a week (It may be narrower than that) and then as the OP experienced, gets too bitter to enjoy.Blueberry sounds like it could be fun!