Peyton is top 5 all time. I'd put him behind Unitas, Montana and Brady (used to have him above Brady but Brady's last couple of years have been great and put him over the top).
Peyton played in a dome most of his career and played in an offense that relies on down the field timing routes. He throws to a spot well before the WR even makes his cut. He never had to worry about weather, wind, and could perfect this kind of offense.
The playoffs are kind of a different game. The 3 best offenses I ever saw were the 1999 Rams, 2001 Rams and the 2007 Patriots. The 99 Rams were the only team to win the SB, scoring 23 pts (plus only winning the NFC championship 11-6) while the 2000 Rams lost the SB only scoring 17 and the Pats just managed 14 in their loss. Points are just tough to come by in the playoffs. The refs let the defenses get away with a lot of hand-checking and bumping of WRs which throws off the timing routes that would be flags in the regular season. Granted the last 3-5 years they've been calling those penalties in the playoffs more now but still allow a lot more leeway. Plus you can hit the QB harder and not have to worry about getting flagged. Then there is that cold weather thing. So the advantage usually lies with teams with good defenses that can run the ball, and use a short safe passing game come playoff time. Elway didn't win anything until he finally got a running game and a defense and Aaron Rodgers is kind of in the same situtation himself.
So yes, he is an all time great and probably the best regular season QB of all time for whatever that is worth. He's also bit unlucky running into the greatest team of this century on multiple occasions. That being said there is no excuse for losing to the Saints in the SB and losing to the Steelers in the 2005 AFC Championship.
