[andreasvc]

That rant is certainly not definitive, he clearly has a chip on his shoulder. He lists a lot of reasons why Esperanto is not a perfect language, but (obviously) no language can be; when a language is constructed people suddenly set way higher standards, but this is not reasonable and leads to endless bikeshedding.

Still, I'd say Esperanto is an interesting case because it is undeniably the most successful constructed language, with the longest continuous (still continuing) history. It is interesting to learn it for that reason alone, and as far as learning second languages go, it is also one of the easiest to learn. That could make it a useful first step towards learning other second languages.

Why hasn't Esperanto caught on with more speakers? Maybe it has something to do with the reasons in his rant; personally I find it much more likely that it's due to network effects. Even a "perfectly" constructed language would be very unlikely to win over the vested interests and inertia of people.