FYI: I'm going 100% opinion here, so if you agree/disagree, that's fine. Let me know what you think
At 97 pieces, Kopaka is a pretty good value for his price, at about 20.6 cents per piece, USD. As with all constraction sets, he is obviously an exception for my preferred 10 cents per piece in System sets.
Aesthetically, Kopaka is my favorite of the six Toa so far. He appears very bulky, contrasting with his more slender G1 appearance. The single blue pin blends in decently with his colour scheme, but the two red axles and the yellow gear are distracting. Thankfully, one red axle and the yellow gear are completely hidden from a full frontal profile. The combination of gold, white, and translucent blue suits his element very well, and they all blend together nicely. However, I do not like the silver on his torso, as it adds another colour to his already colourful appearance. If this piece had been white, or there was more silver to balance it, Kopaka would look much better. I do like the spear and shield idea, though I think the shield may be a bit too big for his size. Of all the Toa, I think his gold mask looks the best while on-character. The gold fits nicely into his colour scheme, but, unlike Tahu, doesn't seem too overwhelmingly gold.
Along with Onua, Kopaka uses some stickers, this time on each upper leg. While the stickers do look nice and add always-welcome texture, I feel that stickers were COMPLETELY unnecessary. While Onua uses stickers due to his massive chest piece, there is no reason these pieces couldn't have been printed. This is not major in anyway, however, and should not affect your decision.
For playability, I think Kopaka has a bit less than Tahu or even Pohatu, the other two that I own. This is largely due to limited posability as a direct result of all this extra bulk. Kopaka has a gear function in one arm, the one that holds his spear. This is greatly hindered by his large shoulder pads and the new shells on his upper arms. It is good enough to replicate quick stabbing motions with his spear, but don't expect to get any more than 150 degrees of motion, unless you plan on re-positioning his shoulder armour. I have to agree with Var on how he holds his shield, as it is hard to pose, especially with its sheer size. Also, the added leg armour hinders his knee bending, but then again, you may not want to bend his knees or the shield will look awkward.
For his adrenaline mode, the skis seem a bit impractical, but otherwise look decent on his figure. Thankfully, the spear isn't as long as I originally anticipated, so it doesn't look awkward having it in one hand without something in the other.
For Kopaka's power-up mode, it is extremely simple, as you are only making modifications to his weapons. The spear is shortened, the tip is replaced, and a saw is attached. His shield is completely discarded, (but could still be used for the skis) and is replaced by the Protector of Ice's shooter weapon. I think the power-up mode looks great (ignoring the added yellow pieces), but the unarmed Protector looks pretty pathetic
The verdict: This set is well worth the $19.99 USD. I think that this is a great re-imagining of the G1 Kopaka and captures his overall look very well. The power-up mode is my favorite out of them all, and adrenaline mode looks pretty cool, though ultimately kind of boring to me. The posability is a bit limited, but it makes up for this in looking great. I give this set an 8.75/10, definitely recommend.