Prior to watching this, I had seen 'Air' which is another made by the same company. 'Air' was the first thing that had ever brought a tear to my eye, I considered myself as emotional as a stone wall when it came to watching things like films and TV series because I couldn't connect with the characters but for some reason I cannot explain, I was simply captivated by 'Air' whether it was the animation, the voices, or the story, it was incredible.
I truly believed I would never experience something greater... and then I watched 'Clannad'. Clannad is split into two parts (Series), the first revolves around Tomoya Okazaki helping Nagisa Furukawa re-establish the theatre club and as a result become better socially as they meet characters along the way, I won't divulge any further about what happens in the second part because it all builds up from the very start.
Prepare your heart for an intense emotional roller-coaster that never stops until the very end. In a lot of series, you can often find episodes that are somewhat irrelevant or weaker compared to others. Fortunately this doesn't occur in 'Clannad'. Characters are explored in incredible depth, not just the main characters either, but all of the peripherals too.
The characters are simply unforgettable, the OST (Original Soundtrack) is incredible and fits seamlessly with the entire series but 'Clannad' strikes hardest with its beautiful and incredibly touching story. I shed so many tears while watching 'Clannad' and it felt like a truly cleansing experience.
While 'Clannad' would be the first Anime I recommend to someone, the story can be quite difficult to understand in its entirety due to the unconventional subplot that is often seen in Anime that prevents them from being immediately accessible and I don't wish anyone to have a tainted experience of it by not understanding it fully. However I believe anyone that has even a decent experience of watching Anime would be able to understand it fully and appreciate it for what it truly is. A masterpiece.