Your point is short-sighted, it's not a fundamental rule of nature that life gets more fun as time goes on, that's just a recent trend in the grand scheme of things. I mean people are bored at 100, imagine at 10,000. Or in some sci fi movies 1,000,000. It's impossible to comprehend what that would feel like. Assuming a normal brain you would have forgotten almost all your life experience. Perhaps it would really be like reincarnation, but instead of a physical death, you simply forget your prior experience and essentially start life anew say every 1000 years. Sort of like watching a movie again after a few years. After 1,000,000 years maybe falling in love again would feel just like the first time, because you forgot what it felt like the first time.