You looking at AC? I played more or less every second one, and the overall story is super convoluted, but each game plays well enough by itself as well. I missed AC2, but I did play AC: Brotherhood (kind of AC2.5 really), and it was way better than the first game. I missed Revelations, but I did play AC3, I have now also picked up AC4, which I will play after The Last of Us.
Each game builds on the previous one and adds some new aspects to the game, so it's been getting more and more interesting. In AC3, they introduced the naval missions (testing the water for the sailing stuff - har har), and new since AC:BH was a whole economy with crafting and trading goods, and building up a community of people to craft said goods. In BH, they introduced extra assassin recruits that you can call to help you in a fight and also to send on their own missions to make money and improve their stats, and they were still there in AC3.
The main problem with AC1 was that missions, especially the side missions, were really repetitive and boring, and they fixed that I think with AC2.