I've yet to reach endgame as BLM, but so far my experience hasn't been great. That isn't to say I haven't been enjoying it. Big crits are very satisfying. Having to properly learn mechanics is nice - playing BLM is forcing me to get better at the game.
However, the overall experience is mired by small yet annoying issues. Getting screwed by mana ticks, having to let TC drop off because you can't fit it into your fire phase, the boss targeting you with stuff 6 times in a row, etc.
So far, when it comes to "real" content, I've run some EX trials. In those EXes I felt like I could've been doing far more for the group as a different DPS. Sure, I did good damage, but I likely could've prevented those low % wipes by making everyone else do more damage.
All that in mind, BLM is still very fun to me. It's a bit clunky sometimes, and I'd like to have some utility, but I'll still play it anyway.
Until I get to raid content and have to switch jobs to get in...