It is kinda great. But years pass and one gets bored of hearing "Go Pikachu". I recomend to leave it to your little brothers. I am sure one can get fun by other series.
I honestly believe that Pokemon can be fun dipite your age. I'm not a little kid anymore, and I'm still a huge fan of the series. While it's certainly not suited for everyone, I still think it's an incredibly fun game. It's pretty much up to you weather you like it or not, but I'd reccomend it.
Once you understand some of the game mechanics, E.G., Evs Ivs etc. it can add a lot to the complexity of the game, and this makes it a lot more interesting. However, the multiplayer is still way better than just plodding through story mode ( although you should definetly finish that)