http://en.wikipedia.org/wiki/Crystal_MonstersReception
Lucas M. Thomas of IGN criticized Crystal Monsters for being "unbalanced in monster selection, and boringly repetitive." [1]
Marcel van Duyn of Nintendo Life said "Although it might be almost sickening to Pokémon fans to see how similar this is to their beloved franchise, we can't really be too critical of it. It's only 500 DSi Points (300 less than most Gameloft games), and for what it is, it's actually quite a decent, if simple, imitation." [2]
KnucklesSonic8 of Wiiloveit said "In summary, I'm not sure I'd call Crystal Monsters a rip-off exactly, and even still, what do you expect for only $5? It's a decent romp that RPG fans should enjoy, as surprisingly as that may sound. There's not a whole lot of depth here, and there's a significant number of flaws that prevent this from being a good game. But Crystal Monsters can be fun to play if you don't take it too seriously."[3]