As a 19 year old rookie with no college playing experience LeBron was in the top 15 in the NBA in all of the following:
PPG
SPG
Minutes
Ass.
Points
APG
FGM
Steals
He was in the top 5 in all rookies in all major statistical catagories. Of course, his ROY Award means nothing too I'm sure. Carmello had a better cast surrounding him than LeBron did, and LeBron had the Cavaliers in the playoff race until literally the last few days of the season. He also doubled the Cavs wins from last season (Mello did the same I know) and generated interest in a team that has had a dead fan base since Brad Daugherty left. Yeah, I said Brad Daugherty.
None of that says overrated to me. The difference between what Mello did and what LeBron did, was that Mello came in with the experience of playing against something other than HS players. Going through the tournament (and winning it) is one of the single greatest learning tools for an amatuer player. LeBron didn't get that. He made the straight jump, and showed he MORE than belonged. Hell, James joined Oscar Robertson and Michael Jordan as the only players in NBA history to average more than 20 points, five rebounds and five assists per game in their rookie season.
Here's a look at the last few Hyped up HS'ers compared to LeBron in their rookie years:
http://www.kfba.net/Articles/19892.aspx this shows how they don't stack up to LeBron who's rookie line. LeBron had more PPG (20.9), loses out only to Kobe in FT% (75.4), is beaten out in RPG by only Stoudamire and Garnett (5.5), blows them away in APG (5.9), and he also is in the upper half in blocks with .7 PG.
He's not overrated.