There are 2 significant changes in Den-O compared to recent kamen rider series that I have noted so far.
1. Ryoutarou's use seems to just be the channel for the 4 imagin. I really didn't like this idea, as it isn't him fighting off evil. Instead, it's kinda like getting the stunt man out and doing it all (ok, that is what really happens... but...). I'd rather the hero fight. Hope that makes sense.
2. Monsters had human forms on the previous 3-4 kamen riders. It also created a LOT of drama dialogue (hated it). For this story, the monsters come out and simply go on rampages.
I'd hoped there was a more organized evil power, but at least it isn't 18minutes of non-understandable dimensional-talk, 4 minutes of cleaning laundry, and 10 seconds of fighting, that cuts at the end. So I'm happy for this change.