My 4 year old son likes pretty much all kinds of cartoon characters, from the more recent Ben 10 escapades to the old classics such as Tom & Jerry. He recently started watching the 1990's "Action Man" cartoon and immediately wanted to be Action Man like any other child his age would.
On Christmas morning he had a few figures to choose from, such as Ben 10 creatures, Iron Man, WWE figures, Toy Story... however, the look on his face when he opened the wrapping and held his very first Action Man figure was priceless. This thing is durable as hell, he has already battered it in wars with Doctor X, ha ha, and I can see him playing with it for years to come.
It may not have all the flashy gadgets and buttons, but it's all a boy really wants; an action hero where he can make the rest up in his imagination. It doesn't claim to be anything which it's not. If you don't get it, it's probably more your problem than the toys.
It's a boy thing.