It depends on what kind of love you are referring to. In Japanese culture, love is a very valuable concept and has several different words to explain degrees of love. both ai 愛 and koi 恋 mean love, but koi is a longing, passionate love that borders more on infatuation while ai is the more selfless and pure, long lasting love...real love. Aside from this, there are different ways to say you love or like something.
-Suki desu (skii-des) 好きです would mean you like something, it can be used as a strong like
-daisuki desu 大好きです (pronounced die-skii des) is the word from which "suki" comes from. Dai 大 literally means big, so daisuki is a BIG like, meaning you like something or someone very very much. Saying it in this way means "I love you." However, daisuki should be thought of as maybe young love or new love. It is still love but not as serious as "aishiteru" This is probably the most common way of saying "I love you" in Japan. Suki is also very common.
-aishiteru yo (or wa if you're female) 愛してる (pronounced eye-sht-eh-ru) is a phrase that many Japanese people go their lives without saying because they take it very very seriously. Aishiteru is like pure, forever love. The kind of love and bond that can never be broken. If someone says "aishiteru" it means that they love you with all their heart and soul and they are very serious. Think of it as soul mate love.