Have you ever read any of his papers? The guy was a freakin' genius.
Even with 100 years of technology and theory I still find what he
figured out amazing. There is a book that is a compilation of many of
his research papers. It's a little dry, but very interesting. If you
think you're a smart guy, read this. It will make you realize you are
a "little" person as far as intellect and contribution to society are
concerned.

As for his later inventions and "crackiness", most of that was driven
by investors heavily over invested looking for more genius. The "death
ray" was a result of someone's brilliant suggestion of "wireless
electricity". The result was the infamous Tesla coil.