Andrei is a big strong guy with good speed and a sick shot, but he is hampered by poor hockey sense and positioning. He tends to keep the puck to himself and often tries to do too much with it. He would have to play a simpler game to be effective, he'd have to rely on is shot more and get into the open ice more often. If he could do that, he could become a Sykora-like, «stealthy» goalscorer, but right now his game is not polished enough for the NHL.
Sergei has made smarter choices so far and he already has adapted quite well to the North American game. He is every bit as skilled as Andrei and he is even faster than him, but he is not as big and his shot isn't in the same ballpark. Still, he has a lot of offensive flair and he has proven to be a much more adaptable player and person than his brother. I wouldn't be suprised at all if Sergei were to become a better player. He could also hit a wall and head back to Europe, but hey, some late round draft choices actually turn out to be pretty good player (Svatos?), so I think this guy worth keeping an eye on.