I absolutely love the original. Predator 2 is fun, action packed, and very well done, but failed to capture the magic of the first. Predators I also found rather enjoyable, but it too failed to reach its full potential (BTW, technically Predators is Predator 3, just without the 3 in the title).
I too would truly love to see some more Predator films. They could take place in the distant past (a Predator is hunting vikings, forcing the king to send a team of his finest warriors to hunt down and destroy the beast, thus spawning the legend of Beowulf and Grendal), the present (a Predator is hunting US soldiers and Al-Quida terrorists in Aphganistan), or the distant future (a Predator is hunting human colonists who are trying to tame a wild and dangerous alien planet for mass human colonies).
While I don't disagree that maintaining the Predators' mystique is probably the best way to go, I do enjoy seeing little snippets of their culture where I can understand their mind set a little more (their code of honor shown in Part 2, the clan feuds shown in Predators, etc).
People keep asking for a movie set on the Predator's homeworld. I think this is a mistake. First, you lose absolutely ALL of the Predators' mystique by going this route. We don't get a little taste of their culture, we get the whole damn meal. Secondly, the only way that can work is if Earth were to launch a full scale invasion of the Predator homeworld. Then it won't be a "who's the predator, who's the prey" storyline. It's just simply a space war movie between humans & Predators. It's Star Wars, or Battle Beyond The Stars, or The Last Starfighter, but certainly NOT Predator.