I played both last year. They're pretty good and are among the few adventure games that are reasonably modern. Both games' plots contain things that don't make sense or are left unexplained, but my overall impression was good. I think BS4 is definitely better though and probably the best game of the series.
Note that in case you have a CRT, BS3 will only work at 60hz and nothing else. It took me a while to figure out why the game was not starting for me, but this turned out to be the cause.