I often hear Metagross [Plasma] compared to Pidgeot (EX: Fire Red/Leaf Green): both are Stage 2 Pokémon with a non-attack effect that allows you to add a card from your deck to your hand, once per turn... period, as opposed to once per turn per copy of the Ability.
Pidgeot was an amazing card, and was legal when I was actually, actively competing in the game (though a lack of travel funds kept me from attending anything large) and I can tell you first hand, it was a card you either played or you countered... and sometimes that you even played with counters, to shut it down once you had a good set-up. This was because the card was broken. Few people agree with me on this, but I stand by it: Pokémon cards seldom have significant "to play" costs, and it was terrible having a fun strategy shut down because your opponent could grab the perfect counter card at the drop of a hat. This includes generic "come-from-behind" cards like Scramble Energy.
Metagtoss [Plasma] is in no way broken. Pidgeot existed during a time when overall offense was slower and rarely hit anything close to modern damage output, and yet Evolutions were faster (due the original Rare Candy text and rulings); this meant even when you had a good offense, it was very hard to outpace the set-up provided by Pidgeot. As it could fetch anything and often survived for two turns, it was also easy to "break even" with two uses of Quick Search - the failing of many "set-up" Pokémon is that they take too much effort to set-up themselves!
Metagross [Plasma] has proportionately about the same HP, but it can only snag Team Plasma cards. There are many potent Team Plasma cards, but not enough to build a full deck using just them. Most problematic is that there is only Plasma Energy for Energy cards, and while there are Supporters, said Supporters aren't the best for reliable set-up. I do believe Metagross [Plasma] has untapped potential, but I do not know how extensive this is; you need something where a Bench-sitting Stage 2 (the attack isn't worth using) speeds it up/makes it more reliable than the next equivalent build. Frankly, I think they should have allowed the effect to be used more than once-per-turn-per-copy.