I don't think he's a shoe-in or a first ballot yet, but I definitely think he is a Hall of Famer.
He's played 10 seasons and missed only 56 games in that entire time. He's averaged 23.1 points per game (which, by the way, is good for 21st ALL TIME and is ahead of Dirk, T-Mac, Ray and Duncan), 6.4 rebounds, 3.9 assists and 1.6 steals. He's 77th all time in points, ahead of Hall of Famers like Worthy, Dumars, Sam Jones, Walt Frazier, Dave Cowens and Tommy Heinsohn. And deserved or not, winning a championship and a Finals MVP jumps somebody up considerably.
The fact that he's never made All-NBA First or Second Team has nothing to do with it. He should have made one of those teams, he just didn't get the notoriety because his teammates were so bad or he was just snubbed. In 01-02, he was third in the league in scoring, played all 82 for a 49 win team, threw in 7 boards, 3 assists, 2 steals and a block game, but still only managed to make the Third Team. T-Mac made the first team playing 6 fewer games for a team that won 5 fewer games, with stats of 25.6-7.9-5.3-1.6-1.0. Kobe made the first team over Pierce even though the only stat where he was ahead of Pierce was assists (5.5 to 3.2) and he had Shaq on his team to help that squad to 9 more wins than the Cs. Ahead of him on the second team were Allen Iverson (31.4 points, but on .398 shooting, 4.5 boards, 5.5 assists, 2.8 steals, all impressive but he only played 60 games on a 43 win team) and Gary Payton (had 22 and 9, team won 45, 4 less than Boston). Chris Webber also made the second team despite only playing in 54 games.
Pierce should have made at least the Second Team in 01-02, and probably 02-03, too, but got snubbed because he had no rep up to that point. By the time he had a rep, the Celtics were worse than before and he could get no love. Finally, this year, when he put together his best all around season and captained his team to an easily league-best 66 wins, he gets relegated to Third Team and even finishes behind Carlos Boozer. He should have been Second Team again this year, but got no love for no good reason.
Bottom line, Pierce is a Hall of Famer. No doubt in my mind.