I bought the Genesis the week it came out in the U.S. I still own the console and all three (+Knuckles) original cartridges. I have the the console originals on several platforms.
I say this not to brag, but to show that I'm at least passingly familiar with the originals.
My question is... what do you mean by "missed the point of the Genesis games?" The best I can figure is that they are supposed to be tight and fast (to show off the prowess of the Genesis system) platformers with a bit of exploration and lots of racing/timing. Is that not what Generations does?
As I mentioned before, to me, the Genesis titles were almost more about the exploration, level design, and "organic" nature of the gameplay (which is essentially to say that you could pretty much make your decisions on the fly and the games would very rarely harshly punish you for that) than they were about the speed. The post-Genesis titles, even through Generations (I haven't tried Lost World or Boom), generally have more linear levels (to the point where some of them, like Colors, having large swathes of levels playing out as little more than glorified QTEs). The level design, even in Generations (which I'd agree has about the best of the lot), just isn't as good, and I really don't think they've ever gotten the hang of 3D platforming. And, in the modern games, you really can't just up and decide to switch gears in the middle of what you're doing. If you see something interesting in the Genesis games, you could almost always go back, look around, and try to find the way to get to it, even if that path is almost all the way back at the beginning of the level. In the post-Genesis games, including Generations, you really just have to start the level over. Similarly, if you screw something up, there's generally no way to do it again without restarting the level.
Even in the games where it does some or all of this stuff tolerably well, I can't shake the feeling that it all takes a back seat to the spectacle of speed, and that where solid gameplay might interfere with that speed it would be (and often is) sacrificed.
That's my experience, at least. I've never actually finished any post-Genesis Sonic game, to be fair; and while I like to think I'm
relatively objective about the matters in question, I'm honest enough to admit that I'm certainly more subjective about it than I could be.