Well, Poser users have gotten pretty good at getting decent renders out of P4, so there's plenty of room to learn and enjoy P4. Bryce, which is oriented toward doing landscapes, was originally made by the same company that did P4, though now both have different owners. Vue d'Esprit is similar to Bryce. The rendering engine P4 uses is much like those used for videogames; the engines in Bryce, etc. are capable of getting more realistic renders, but of course cost money and take (usually much) longer to render a picture. If you haven't seen what Bryce or Vue can do, stop by their Galleries here;-)