The first four ramps are steep, after that it eases off.
How hard can it be? Depends how much you like climbing and how quickly you want to get up I guess. Its easier than other climbs in the area because its not that long (comparatively speaking) and the plaques at each bend – not to mention the slogans painted on the road – give you something to read and think about as you go up, so it doesn’t get monotonous. Anyway, its l’Alpe, you’ll be excited just to be there. Plus, the scenery is jaw-dropping and the higher you go, the more you see.
I did it last year in a real hurry – was en route to Marseille from Bourg StM to fly home, had to also stop at Bedoin to return a bike. I’d planned for enough time to dump the car at Bourg d’Oisans, scoot up it, few photos then back down, but that was before I hit traffic approaching Grenoble. Decided to go for it anyway but had to hammer up it then drive like a maniac all the way south and made it with minutes to spare. I was well under the hour for the climb! 😀