Depends, I get much less of a high than many people, due to frequency of use - however, I've never quite understood the people who say that it makes them hallucinate and trip out madly. I've never had that, on my first time or after 8 or 9+ in an evening, though accept everyone feels it a bit differently. I'd say it depends very much on who you're with and where you are, and on the sort of weed you're smoking - you can either get a very buzzing high, involving a lot of laughing and crazy ideas that sound fantastic at the time, or find yourself in a really monged state where you can't really do anything except sit and observe what's happening around you, occasionally marvelling at something seemingly amazing.
I'd say if you've never had it before, you don't want a whole spliff (king size) to yourself, you'd be best off sharing the experience with others anyway. Hell, I know people who've been smoking for years and still can't stomach a whole one - it affects everyone differently, so don't go overboard your first time and just assess your reactions to it.