For me, the limitations are the entire point. But then again, I think I approach characters differently than many here. I don't have a mechanical "build" in mind or even a mechanical niche. I generally start with an archetype--what FATE would call a "high concept"--picked from the "supported archetypes" of the game system and then go from there. Generally, I have little in mind for where I want the character to go past the starting point, just some open ended motivations and unknowns. In part, that's because discovery (what's over that hill?) is one of the major sources of fun. I want to see how the character evolves both mechanically and personality.

And mechanics only exist (for me) to bring out pieces of the character--since I don't have a power set in mind or even a really strict theme, I can play it by ear. Systems where I can't and have a reasonably effective character (aka 3e D&D and PF, both versions, all of which demand "build thinking" from the get-go) annoy me.

So for me, a system, world, or even campaign having strong thematics and restrictions enhances my fun, as long as the overall thematics is something I enjoy[1].

This also makes me prefer class-based systems over point-buy, since class-based systems inherently (or at least when they're not trying to do point-buy, but badly[2]) promote strong archetypes. The Noble Paladin, Guardian of the Weak. The Strong Barbarian, Raging Terror. The Nimble Rogue, Sly Shadow Sneak. The Learned Wizard, Scholar of the Arcane. They clearly say "this is what our game supports and encourages." And I like that.

[1] by which I mean things like "I don't like evil campaigns" or "horror isn't my jam".
[2] often, trying to provide build granularity ends up giving you a menu of directly-comparable things of varying value...but all the same cost. CF D&D spells, where even spells of the same level (and thus cost) vary tremendously even for the same mechanical niche. Or D&D feats, with 3e/PF/PF2 having the worst versions of this. If you're going to do a point-buy, build-a-bear system...go all in. Don't do point-buy badly. Some parallel power-structures are ok, especially when they're truly parallel. So you're not trading off the thing you're supposed to be good at for a shiny-but-weak toy or worse, encouraged to spend your theoretical "versatility picks" on pumping your numbers higher. Or yet even worse, tricked into thinking that you have freedom...when all you have is freedom to make the wrong choice and fall behind. Where if you pick optimally, you keep up with the system's baseline, but if you don't you fall inescapably behind expectations. D&D 4e with the Weapon/Implement Focus feats, I'm looking at you with both eyes on that one.