There are people who still think that "Adventure Time is a kid's show on drugs. And it's not worth my time because it's on so many drugs!" To which I respond, "Just because it might be on drugs, doesn't mean it's a show that makes absolutely no sense."
Yes, to understand this show, it will take some time. But that's pretty much how it worked for everyone who is now a fan. At first, the show starts out as a complete mind fuck for the majority of season 1, and you will most likely feel totally lost. But give the show some time, and there will be parts where you are left in tears. Yeah, the show isn't 100% wacky craziness, but you might think that if you rely only on first impressions. There are times where the show takes some really dark turns even to the point where you don't know what will happen next. And I like plots that are unpredictable.
I'm now at the point where I care about almost every single one of the characters. Why? Because they feel so alive. And by "alive" I mean that they have complex and identifiable personalities.
If you want my best advice, don't take the show too seriously at the start. The show itself will let you know when to take it seriously when it gets there. Overall, I personally see the show as a tribute to a child's vivid imagination. The stories that kids come up when they're "role-playing"(because that's what we're calling it now). The stories, the action, the... ADVENTURE... all of the creativity feels like it come from a child's mind, but in a good way.
If you don't understand what's going on:
Everything will be explained as the show proceeds. As you continue on, you start to see the show being carried by continuity. That's right. The show has its own continuity. And if I said anything about the continuity, it could spoil the show.
Now go! Watch this wonderful series (don't give up after just 1 episode; I notice a lot of people doing that) and you tell me any different.