Bloodthirsty pond faeries: because pixies are boring.
6 fey RHD are not great, and the ability boosts aren't stellar either. However, DR 5/cold iron and resistance 10 to cold and fire make up for it some. The +4 bonus to Bluff and Sense Motive are welcome, but not incredibly useful.
The special abilities (the reason why fey are playable at all), are... okay. Blood Drain is near-useless on something with worse grapple than your average human rogue and Water Breathing is decent. Water Symbiosis is nothing but an annoying anchor to get rid of somehow (Acorn of Far Travel, Ability Rip, losing the ability to suffocate). Finally, there's the rather interesting Beguiling Song, which sadly only functions in a tiny area around the glaistig's bonded pool and is nearly useless in most campaigns.
Finally, the SLAs. At-will Hypnotism is okay-ish at ECL 6 and rapidly becomes weaker, Fog Cloud and Dancing Lights have some niche uses but are otherwise not much better. At-will Suggestion, however, is probably the most interesting part of this entire creature, even if it doesn't make it PC-worthy. 1/day Water Breathing is nearly useless in-game, unless your party has only one nonaquatic member.
Verdict: -0 LA*, with Water Symbiosis being the problematic ability one needs to get rid of for this to be playable. If your entire campaign takes place within 300 feet of a single river or lake, I guess you could assign +0 here.