Y'know, if I could have picked two moves within reason for Rapidash to learn, Wild Bolt and Low Kick would have been way up there. They are great additions for sure.
It isn't fair to compare him to Arcanine because there's no way they're going to end up in the same tier. They weren't in 4th gen and that's not likely to change. Comparing him to Entei is more appropriate but remember that Entei can only really be compared to Rapidash if he uses Flare Blitz in which case he a) needs to be Adamant and b) needs to use Pressure. That means Rapidash has a significant speed advantage over Entei and the ever-useful Flash Fire ability.
The Choice Band set looks awesome now...I used to hate being forced to run Return, Hypnosis or even Double-Kick. 100 Atk is reasonably modest by todays standards but consider that with Flare Blitz/Megahorn/Wild Bolt/Low Kick Rapidash will be hitting the majority of targets for at least 180BP. With two recoil-inducing moves and a SR weakness don't expect him to live too long though. Especially with that poor base HP.
I was secretly hoping he'd evolve btw. With him already being a mythical creature (he's a unicorn, I dunno why GF insist on passing him off as a horse) I would have liked to see him evolve into a Pegasus. How cool would that be!