It's protected from monster effects, but at only 1700 ATK it can be easily dealt with in battle anyway (and via Spell/Trap effects too).  But the main appeal to this card is not the power or card advantage, but rather the potential combos it can setup.  Since it summons straight from the Extra Deck, it basically gives you a free discard whenever you want to fill up your graveyard power.  It being a Tuner also opens up even more Synchro combos.  It's what you make of it, but I'd keep an eye Tatsunoko.
 
3/5

Tatsunoko is a great combo piece for Synchro monsters. It comes in with Level 3 Water Wyrm-type Synchro/Tuner monster with 1700 Atk and 500 Def. These are ok stats for a Level 3 monster. I don't think that it's Water matters. I believe what matters is that it is a Tuner and a Synchro monster. Tatsunoko's effects make it easy to utilize that feature.

I am going to start with the second continuous effect. Tatsunoko is unaffected by other monster effects. That is handy and a good form of defense. The main effect is that if you are going to Synchro Summon with this monster, you can use 1 monster in your Hand as 1 of the other materials. I love that it doesn't matter how this card is summoned. If it hits the grave and you revive it, you can still use a hand monster to Synchro Summon. Tatsunoko makes getting monsters that require Synchro/Tuner monsters a bit easier.  

Score: 3.5/5 I would score it higher if it were a Dragon. Still a good combo piece.

Art: 3/5 It's cute.

-WarlockBlitz

Oh my Gawd, it's adorable!!!

And it's quite useful; it too is a Tuner, and it's uneffected by other monsters' effects which means you'd only have to worry about it being steamrolled in battle if you need to keep it on the field a little while longer. And why wait, anyway? It allows you to Synchro Summon... from your HAND!! Could this be the start of a whole new wave of Synchros? Or is this little seahorse- sorry, sea Wyrm- in a league all its own? Time will tell.

Now come'ere, you little squishy, I wanna pinch your widdle cheeks and kiss your face- OW! ...Note to self: baby sea wyrms have teeth. And they hurt.

Final Score: 4/5, Synchro decks only