tl;dr: A solid, though rushed, adaptation of a story with amusing and likable characters and decent action.

This is the manga adaptation for the light novel that was also adapted into a number of popular anime seasons. I've already seen the anime version of the parts this manga adapts, some of its seasons multiple times, and thus it's hard to really judge the manga on its own and not in comparison to the anime so this will somewhat be a comparison of the two.

This manga has the same cast of incredibly amusing characters who are all really likable and enjoyable just to see interact in various circumstances, especially the main character Issei who is absolutely ridiculous but hilarious and amazing. There were some differences though, such as that Rias felt like she came through as less majestic, which I wasn't fond of. It has the same solid plot with solid world building regarding factions, history, and such. However, it was paced much faster and a lot was removed or modified to shorten it, and with that pacing it manages to adapt approximately the first two and a half seasons, which is about 4.5 light novels, in 11 manga volumes.

The ending of this manga was completely different from the anime, in that this manga adapted a portion the anime didn't but modified that portion to serve as a more complete ending even though it was only the beginning of a longer story in the novels, which felt like a strange way to end things. I also think that as a result of the much faster pacing, character development and relationship development doesn't come through as well, even if it does manage to have all the major events, but at the same it's hard to judge because I'm already really familiar with the franchise and sort of have those events already ingrained mentally for lack of a better way to say it. 

The art is pretty solid all the way through and fit well enough. The action comes across decently enough. The characters were more of a mixed bag wherein I'd say the anime looked better but the manga's art is still pretty good in and of itself. All in all, I think it's a solid go through of the story if you're already familiar with it and want to re-experience it, but I think the anime or light novel would be better as introductions to the franchise.