As someone who has all three Kobold monster books currently, in pdf and on Roll20, I can say I like them better than the core Monster Manuals. The art is top notch, there is a lot of variety in the monster design, and some of them are just plain MEAN. I would say on average the critters are more dangerous than core monsters of the same CR. My guys were fighting some umbral vampires last night that did 4d6 cold damage with a touch and drained 1d6 points of Strength automatically. If I had rolled a critical hit someone would have died, as I'm pretty sure that Strength drain would double to 2d6, and the people getting touched were weak spellcasters. And, unrelated, it makes me miss the days of actual Touch attacks where your armor and shield doesn't matter.
Marc, I DO think they're better. Also, for players who are jaded by the old Monster roster of D&D, the Kobold Press line offers hundreds and hundreds of bastards to either kill or run from, and players don't have any idea what they do. My players are still terrified of exploding toads after meeting them at 2nd level. Also, the art is often so good that I Photoshop the entire picture into a token and use that online. The little round tokens are fine, but they so often leave out the best parts of the artwork.
