The last few Tarzan books get kind of bad too, unfortunately, because Tarzan's characterization seems to shift towards the movie version of the character (which is lame in comparison) and most of the female characters turn into vapid stereotypes.
The early Tarzan books are all fantastic though, and I highly recommend them. But I tend to prefer his Martian series (which is also available for download here). They're more exotic and consistent, except for the last "book" which is really one unfinished ERB story and a second story that was written by his son. They're probably not quite as Indiana Jones-ish though, unless the pseudohistory of Mars counts.
