Hmm. Not sure how I feel about that. Certainly not overwhelmingly positive.
Personally, I felt that increasing the level cap in Fallout 3 was the mistake, rather than having one in the first place. But that's because it was a "gain X skill points/level" system, and having too many levels took away any need to balance what you picked. Also, the original perks (up to the "capstone" lv20 ones) were clearly balanced around 20 levels. Being able to level further, and take more of the fancy lv20 perks? Meh.
I also didn't have a problem with the fact that the game ended. Yes, the ending was poorly written, but that's a separate issue. Me, I just did the final quest, reloaded my previous save, and kept playing. There were no "OMG, can't keep playing!?!?!" issues.
One thing I desperately hope is that the super-over-leveling in FO4 is optional like in Skyrim - if you didn't want to partake in the whole Legendary thing, you didn't have to. If FO4 just keeps counting up your XP and giving you more & more levels, there'll be no way to avoid it. And that would svck.
Personally, I don't focus on the "leveling" as a central thing. Playing at the level cap, or with maxed out skills, is just fine for me. (Ex: my first play of Fallout 3, I hit the level cap before even getting to GNR. I finally got around to finishing the game at around 25 hours. I played that character another 50 hours beyond that, before making a new one. So, 60+ hours without allocating new skill points or perks. And that was fine with me. Honestly, I've never really understood the viewpoint of "I can't get more levels, why keep playing?")