One word to sum it up? Charming.
Costume quest is a turn-based RTS at heart and enjoyable from start to end. I honestly can't think of any con except maybe the low difficulty.
Costume Quest comes with achievements, collectibles, spells, monsters,costumes, bosses. What else does a game need in the end?
Also comes with a free DLC and the promise for more and while not trying to spoil the end, it does offer an opening for future development.
My advice, get it, buy it, play it. You won't regret it. Worth every penny.

Man VS Wilderness.
Just like real life. Grab an axe, build a house, get attacked by zombies, goblin armies and jelly monsters.

Gross, fast, funny and did I say gross already?
Story? 4.5 / 5 - Some may call it stupid, others retarded, i find if sadistically funny.
Gameplay 4 / 5 - Only giving it a 4 / 5 simply because at times it may feel like a grind but all in all it's solid, has somewhat random dungeons, interesting and unique enemies, bonus rooms, lots and lots of weapons and items, too many after a while even.
All in all? 4.5 / 5
Grab it if you can, worth every cent.