The truth, as usual, lies somewhere in the middle.
Shanahan, as HK listed, has done some very impressive things. The problem for him is that they all date back 5-10 years, and he's shown no ability to replicate what he did with Elway. What players has he developed? What innovations has he come up with? Since Elway retired, he traded away arguably the best offensive player his team has had - Portis - after only two seasons in which Portis was an absolute world-beater in his system. His post-Elway teams are also 1-4 in the playoffs, and have only had one division championship.
He's a likely HoF'er, but at the same time he's done little in the last decade to remind people why that is the case.
I'll bite.
What players has he developed - Not sure how to interpret this. Let's say pro-bowlers in the post-Elway era - here's the list of skill position/defensive/ST players to make a pro-bowl w/o Elway:
Detron Smith
Trevor Pryce
Brian Griese
Rod Smith
Dwayne Carswell
Deltha O'Neal
Ian Gold
Al Wilson
Jason Elam
Clinton Portis
Champ Bailey
John Lynch
Jake Plummer
You can discount Bailey & Lynch if you want as they were premier players prior to coming to Denver - the same can't really be said for any of the others here. Outside of those two, I'd say that any of the other guys on this list have failed to surpass what they did in Denver on another team.
We can also throw in the outstanding draft of 2006 as well - Cutler, Marshall, Scheffler, and Dumervill are all progressing nicely.
What innovations has he come up with?
Well, for starters, the zone running game was an invention of Shanahan in conjunction with alex gibbs. This basic scheme has been adapted by Houston, Atlanta, GB (I'm not sure who else is running similar schemes). I think it's fair to say that the ZB running game has been a major influence to the game over the past decade.
Post season success (or lack thereof):
While the post-season success hasn't been at a level Denver fans have become accustomed to, I'd attribute that to no home games - well, two home games, where they handed Brady his first ever post-season loss, and lost to the eventual SB champs, Pittsburgh. They simply haven't won the division more than once since 1999. That's the problem right there. of course, this AFCW is the division of the 2003 SB Raiders, the Chiefs w/ Holmes & Gonzo, and LT and the Chargers. The Broncos teams since 1999 have been mediocre, whereas their opponents have been one level shy of NE/Indy. Let's face it - the AFC is highly competitive, the AFCW especially so. While I would have liked to see more wins in the playoffs, I'm pretty happy that Shanahan has been able to roll the team over and remain relatively competitive without a complete tear down and rebuild.