The gemara tells us an amazing story where Moshe Rabbeinu watched Rebbi Akiva lecture was "weakened" by Rebbi Akiva's ability and understanding of the Torah. Finally, when Moshe Rabbeinu heard that Rebbi Akiva attributed a halacha to הלכה למשה מסיני, he was comforted.
Throughout the Talmud we are given tidbits of information that can be pieced together like a puzzle to understand the personality of Rebbi Akiva, his accomplishement, and why Moshe Rabbeinu was initially "weakened" and then comforted.
Pesachim 49b - Rebbi Akiva originally had tremendous antagonism toward talmidei chachamim that he wanted to bite them as a donkey would bite crushing the bone.
Avos D'rabbi Nosson (6:2) - Famous story with Rebbi Akiva being inspired by a drop of water that was capable of penetrating a rock through it's continuity.
Nedarim 50a - Rebbi Akiva is sent by his wife to study Torah and returns with 24,000 pair of disciples.
Yevamos 16a - Rebbi Akiva earned a world renowned reputation and impressed Chanina Ben Hurkenos.
Chagiga 14b - Of all the great scholars who were נכנסו לפרדס, Rebbi Akiva is the only one to go out in peace.
Yevamos 62b - Rebbi Akiva's disciples all die for not showing proper respect for one another, he then chooses five of the greatest minds and teaches them Torah. Rebbi Akiva becomes an essential link on the chain of the mesorah.
Makos 23b - Rebbi Akiva has an outlook where he is able to provide hope for the Jewish people by showing that since the bad prophecies have come true, the good one's are also going to come to fruition. The hope he provides is another essential aspect in the survival of klal yisroel.
Brachos 61b - Rebbi Akiva becomes so attached to the Torah that he can't fathom separating from it, and draws the parallel of a fish being taken from water.
Sotah 49a - When Rebbi Akiva dies, "kavod ha'torah" is gone. This refers to his ability referenced in Menachos to be able to darshen every letter and every "crown" of the letter, displaying the depth and greatness of the Torah.
Sanhedrin 86a - Stam mishna, tosefta, sifra and sifri are all אליבא דרבי עקיבא. Rebbi Akiva is responsible for the existence of Torah sh'bal peh.
In a nutshell, Rebbi Akiva begins from nothing with tremendous animosity toward Torah scholars. He is inspired by water being able to penetrate a rock, that it could also penetrate him. He is sent by his wife to study and spends double the time alloted studying Torah until he returns with 24,000 students. Aside from earning a world renowned reputation, he becomes so attached to the Torah that he compares himself to a fish being removed from water and proudly sacrifices his life for Torah. His ultimate accomplishment is being responsible for the continuation of klal yisroel by providing hope, and being a major link in the chain of Torah sh'bal peh and showing the depth of Torah in that there is much to learn from even the crowns on the letters.
The Shita Mikubetzes (kesubos 40a) says that the disciples of Rebbi Akiva who follow his opinion are called the praiseworthy of the scholars - ורבי עקיבא היה להם במקום משה רבינו אדון הנביאים לפי שהיה כבר נשתכח תורה שבעל פה עד שבא הוא ושנאה.
What specifically was Rebbi Akiva's contribution to Torah?
Ohr HaChaim (Vayikra 13:37) explains that although Moshe Rabbeinu had the tradition of how to interpret Torah She'biksav, such as the understanding of what G-d means by a פרי עץ הדר and correctly being able to identify it as an esrog (as the Rambam writes in his preface to his commentary on mishna), Moshe Rabbeinu didn't merit being able to bridge and connect the Torah Sh'bal peh with Torah She'biksav. Both were given to Moshe mi'sinai, but each as a separate corpus. The person who would be able to connect them had to be someone who was built from nothing and attached himself to the Torah so that he was inseparable. Rebbi Akiva was exactly that, therefore he merited to be the first to connect Torah shebiksav and Torah she'bal peh and show how much of the oral torah is hinted to within the written Torah. This is why Moshe Rabbeinu feels so "weak" upon seeing Rebbi Akiva able to darshen the crowns.
When Moshe Rabbeinu sees that his entire accomplishment which was the transmission of the oral torah became unnecessary because Rebbi Akiva was able to draw it all from the written torah directly, he had tremendous חלישות הדעת to the point where he felt that the Torah should have been given by Rebbi Akiva instead of himself. It is only upon hearing that even Rebbi Akiva had to answer something by saying it is a הלכה למשה מסיני and cannot be extracted from Torah she'biksav does Moshe Rabbeinu realize that he himself is the most important link in the chain of the mesorah being the one who brought down Torah sh'bal peh from heaven. It was only through the הלכה למשה מסיני being transmitted initially by Moshe, that Rebbi Akiva had the tools to show how many of them are hinted to within the written Torah itself.