Since nobody else really is, I'll defend sceptile.
The reason I don't like grovyle is because I like treecko. The way most of you feel about torracat -> incineroar or popplio -> brionne is the way I feel about treecko -> grovyle. I liked the little gecko. Grovyle was too different; the tail(s) was totally gone, the entire gecko motif got trashed for a feathered dino motif. Change the colors, you'd have a tough time guessing they belong to the same line. Sceptile looks more like treecko, and takes the good parts from grovyle (the arm leaves/feathers, ditching the long head leaf, the weird bird feet, and two leaf/feather "tails") and combines it with the old stuff that worked (a proper tail, better posture). It synthesizes the two designs of treecko and grovyle without throwing one out, and that's good.
I'm convinced everyone who says things like OP never liked treecko in the first place, or jerks off to Mystery Dungeon in their spare time. Explorers of time/darkness/sky are great games, and grovyle's a good character. It's just not a good treecko successor, in my opinion.
