Kage appreciation post! (I'll keep it brief, I promise)
The First - Senju Hashirama
Hashirama is definitely one of the best characters in the series, and worthy of his God of Shinobi title. I love how his signature ability (Wood Release) doesn't seem like it would be all that special, but it's ended up as a more coveted technique than the Sharingan or Byakugan. I also love how he's such a down to earth, approachable, and human character; really atypical of someone as powerful as him. His relationship with Madara is tragic, but really shows the extent of his mercy and his desire to understand one another and live in a world of peace.
The Second - Senju Tobirama
Like I said before, Tobirama might be my favorite character. He oozes style, and he probably has the most impact on the ninja world out of any other character. He's responsible for Edo Tensei, Flying Thunder God Technique, Shadow Clones, the Uchiha segregation in Konoha, and I'm pretty sure he came up with the ninja school system, too. His water release is amazing, and the fight he had when he was resurrected in part I remains one of the best fights in the series. Unlike his brother, he can be kind of a jerk, though...
The Third - Sarutobi Hiruzen
The first Kage we ever saw. The Third plays his grandfatherly character very well, and you can really tell he cares about the village and its people. I feel like he actually stands out the least among the five Hokage, but his Monkey summon and fire release were something. It's a shame he died so early on, but we got to see a lot more of him through flashbacks... he's probably also the kage who experienced the most tragic death out of any of them. Being killed by someone you basically raised as a son is pretty terrible.
The Fourth - Namikaze Minato
Naruto's dad! Pretty much everyone made this connection a long time ago, so it wasn't quite "shocking" to find out his connection to Naruto, but it was interesting nonetheless. Minato's reliance on speed is pretty unique when you compare it to the previous three kages. Minato is probably the most heavily "stylized" of the kages, with his Yellow Flash moniker and teleportation skills. He was also killed by one of his students, although he never found out until much later, after his resurrection.
The Fifth - Princess Tsunade
Tsunade is an interesting character... she's one of the only females in the series that has sex appeal as a part of her character. Her position as one of the Sannin, and her relationship with Jiraiya and Orochimaru, has given us some of the most engaging character interaction in the series. I loved watching her warm up to Naruto and entrusting him with the dream of her deceased loved ones. She's a medical genius
and one of the strongest hand to hand fighters there is... not exactly a combination you find too often. Seeing a female character carry the "powerhouse" theme is always a treat. Also, something of note... she's Hashirama's granddaughter, but we never find out the identity of her parents. What's up with that?