I've stayed at the Golden Nugget. It is the best of the downtown hotels, and the gambling, restaurants, etc... are great. Downtown has its own special appeal: it is a place where I go to relax from the strip, its like taking a vacation from your vacation. Plus downtown's 1950s/1960s atmosphere is great, I think it gives you a taste of the old Vegas. In any other place in the world, the Golden Nugget would be considered a top hotel in town - in Vegas its not a top strip hotel so it gets second billing. But, you get more personal service, better prices on everything, shorter lines, cheaper tables, etc...
I now have two Vegas modes. The first is when I go with an out of control gambler friend, and we get a second floor to the top 2 BR suite at Bellagio. Thats the only way to stay on the Strip, IMO, is when you are treated to the front of the line everywhere. The second way I go to Vegas, I stay downtown at GN, or I also like the Horsehoe - its for serious gambling, drinking, and adult fun. No circus acts, no lions, no cirque de solei, but a good casual relaxed time - and a lot more interesting characters hanging around.