It's more than excellent. Carmelo has always been compared to Pierce, but realize that he's done almost everything better. He's taller, he's younger, he's got a better midrange shot, he won in college, etc. Pierce through the same seasons was better at drawing fouls and shooting the 3.
Pierce has generally been a better player than Carmelo(through equivilent career stages. Carmelo is better now of course due to the age thing). Pierce has always been a better defender(Kansas actually teaches you well here), although it wasn't as noticeable due to his teamates and him carrying the scoring load. When he got better teammates, his defense improved, which hasn't really happened with Carmelo. He's also been a better passer, rebounder, 3 point shooter and much more durable.
I would agree the Carmelo is not really an AI-like volume scorer though. He's slighly over-rated(mainly due to being compared to Lebron, when it isn't really close). He's a very good player and could be significant piece on the right team.
That said, they are close enough that Pierce is probably a good comp. If you got 2 other players of close to the same level then you have a darn good, possibly championship-contending, team(CP3, Carmelo and Amare...maybe; I'm not a huge STAT fan, although Chris Paul might be good enough to make up for it).
If I were the Knicks, Carmelo's health record would worry me. He's been around a ~70 ish game a year guy, and it seems like those guys sometimes start to have real problems as they get up in age(sometimes they don't), but it's something to be wary of.