I guess I'll extend my thoughts on each game a bit.
Superstar Saga (SSS) - Everything felt right to me here. The battles were fun, I liked the overworld, and the crazy adventure. While not perfect, it is definitely my favorite in the series. A.
Partners in Time (PIT)- Honestly, I felt that this game was the closest to capturing that "feel" of SSS. I loved controlling all four characters in battles, the Bros. Items, and the overall plot of time traveling. I think the final area might have dragged on a bit from what I remembered from my last playthrough a few years ago, but otherwise it is another good game in the series. B, but leaning towards A.
Bowser's Inside Story (BIS) - I think this is were the games started to experiment with gimmicks, but I felt they were good for the most part. Bowser was a good addition to this game, and the giant Bowser battles was decent. (But I could have done with not having to blow into a mic). I like the concept of being inside bowser and seeing how the events inside would affect Bowser. However, some of the minigames were annoying to play, like the nose minigame. Some of the bosses were also annoying to fight, like Junker. The bros moves aren't as fun to pull off, but Bowser's specials do sort of make up for that. This is still a good game in the series. B.
Dream Team (DT) - The battles and moves are fun to pull off and the Luigi Giant battles was kinda okay. Going into dreams was an interesting thing, but I felt the plot wasn't as interesting as the previous games. I think was hurts this game for me was the length and pacing of the game. Things tended to drag alot in this game and I had to take breaks before I finished it. Overall, I think this game is okay. C.
Paper Jam (PJ) - Despite the battles being fun, I couldn't even force myself to finish this game. I was really meh about the Papercraft battles and I wasn't digging the Paper Toad hunts. I would have liked to see the characters go into the Paper Universe or something. D, but I might lean towards F since I didn't finish it.