None of the cards people have been mentioning so far in this thread (Rayquaza, Magnezone, Electivire) other than MT Pikachu help you fuel Voltage Shoot since the discard must come from the hand, not other Pokemon. SF Raichu's Burst Ball is the attack that combos with those cards. However, it is hardly the main attraction.
Voltage Shoot isn't easy to repeatedly use unlike Kingdra's Dragon Pump, which seems to be a similar attack on the surface, because it is very specific (you must ditch 2 electric as opposed to 2 of anything) and unfortunately there is no easy way to get all of those energy back into your hand/deck later whereas Kingdra has Aqua Stream to put as many back as it wants while also doing damage. The Raichu player is going to have to rely on Night Maintenance, Conductive Quarry, MT Pikachu with a Pichu underneath, or Energy Restore to get them back.
Having to discard so many energy from the hand means you won't be able to charge up a back-up Raichu very easily. It doesn't help at all that each of the regular Raichus have expensive attacks that require heavy discarding. It is not that easy to recover three energy either even with those Pokemon that can grab it from the discard. You'd have to have 3 Magnezone or 3 Electivire benched, or get 3 heads with Rayquaza (unlikely), assuming you were using SF Raichu and could discard from anywhere. With MT Raichu you'd have to rely on Energy Link or Magnezone. Either way would be very clunky; in fact Magnezone is clunky with Raichu in general if you ask me and so it should not really be considered as a legitimate option. Even if you are able to get 1 or 2 energy back you still have to play one from the hand to use the big attack or Voltage Shoot again, which sets you back on setting up another Raichu or makes it harder for you to fulfill the discard requirement of Voltage Shoot when you want to use that attack. After a while all of this constant discarding and lack of adequate back-up building will add up and the Raichu player will simply face burn out before they can draw 6 prizes, at which point the opponent will take over.
All of this being said, Raichu lv. X is still a card with a lot of potential; the issue is in finding ways to get around the demands of so much discarding while also being able to charge back-up Raichus. Staying alive long enough to get an attacking Raichu lv. X out is also a challenge considering the soonest it can be up and ready is turn 3.
Bottom line: definitely not a 10 out of 10. People who have given this card that rating are grossly exaggerating its abilities.