Well…as others suggested, its similarities to “Friends” are remarkable. Barney is the womanizer (Joey). Ted is the geek (Ross). There’s love triangles involved, they all live together at some point, they have a never-changing hangout spot, and some of the jokes really are good. Some are not.
As with all shows, I think what’s got people hooked are the characters, probably especially Barney. He’s the ultimate “cool guy”, someone who doesn’t let morals get in the way and has the power to manipulate.
Lastly, I think “How I Met Your Mother” writers have been extremely clever by giving the show a purpose – the audience really does want to know who that damn mother is supposed to be.
I loved the first four seasons, though I never thought it was as good as friends. Now, I don’t watch it anymore. I feel like the writing has gotten more predictable, lots of lame sex jokes. I still like Barney, but that’s not really enough. I’ve moved on to “Modern Family”, “Downton Abbey” and “Rizzoli & Isles”.